Salt Production, Use, and Trade
- Alexander AntonitesAlexander AntonitesUniversity of Pretoria
Salt was an important commodity throughout the human past. Although salt (sodium chloride) is essential to human health, the desire for salt in humans cannot be explained by physiological need alone. Instead, both biology and culture drive the taste for salt. The result is that salt was frequently highly valued, with its production and trade important in economic, social, and political systems of the past. Despite this importance, salt is an elusive item to study since it does not preserve well and is mostly consumed. Production sites are often the only places with any discernible remains related to salt use. However, historical and ethnographic material are rich sources of analogies of how salt was produced and traded in preindustrial societies. There are frequently large-scale similarities in traditional salt-making practices despite tremendous technological, organizational, and environmental contexts. These show that salt production technology is mostly robust and fairly simple and that salt can be made with very little investment in infrastructure. As a result, many communities with access to salt sources could be self-sufficient. In the absence of readily available salt, trade networks developed around its distribution over medium and long distances. Consequently, control over this spatially restricted resource was often an important factor in regional politics, and in several cases played an important role in the development of hierarchical systems of power. It is, however, important to discern between specialization production for trade by a small group of producers and production by multiple small-scale producers for their own use, since the archaeological remains of these two different production strategies may look very similar. As a result, archaeologists need to employ multiple lines of evidence in discerning the organization of production.
In contrast to the almost ubiquitous presence of cheap salt in the modern world, for much of human history, salt was a rare and valued commodity that was made and exchanged in all types of societies, from small egalitarian communities (Meggitt 1958) to centralized states (Flad 2011; Potts 1984). While salt is commonly thought of as a condiment, it has in the past been used for, among other things, a supplement in animal feed, curing and preserving meat, tanning hides, fixing dyes, making soap, and as a ceramic glaze and as medicine. The demand for salt meant that it often played an important role in power relations in the past and as a result, its study can offer important insights into the social, political, economic, and ideological systems of the socioeconomic world of the past. The study of salt, however, poses a unique problem to archaeologists, since it is typically consumed and dissolves once deposited. In the absence of written records, the only clues to its presence in ancient society are often the sites of salt production and extraction. This does not mean that archaeological research on salt is limited to reconstructions of technology. A sufficient body of work from different parts of the world shows that it is possible to look at much wider social and economic research topics. Its study, therefore, relies on a combination of literary, ethnographic, and archaeological evidence that allows for an outline of its use. This article presents a worldwide perspective on the archaeological study of salt and salt-making practices prior to large-scale industrialization and its subsequent more widespread distribution.
Humans and Salt
Common table salt (NaCl), is an ionic compound made of sodium and chloride ions. The demand for salt is often tied to human physiology, since sodium plays an important role in numerous biological processes (McCance 1936). There is no consensus on the minimum dietary requirement of salt and it seems that sufficient levels of sodium are found in meat, milk, and certain vegetables (Dethier 1977; Mattes 1997). Humans, like many other mammals, show an overwhelming craving for sodium salts in situations of salt deficiency in the body (Contreras 1980). However, humans typically consume far more sodium than what is needed for normal physiological function (Brown et al. 2009; Dahl 1958, 1958; Hurley and Johnson 2015). Salt gluttony—the craving and overconsumption of salt—may be the result of chemical receptors in the brain that mimic addictive behavior (Kaunitz 1956; Tekol 2006) and is associated with serious negative health effects (Denton et al. 1995; He, Li, and MacGregor 2013; Mattes 1997).
Because salt was traditionally a scarce and highly valued product, it often assumes a cultural significance that goes beyond its dietary and functional importance. Salt frequently forms part of local and regional exchange or tributary networks often serving as a standard of value for other products or services (Parsons 2001, 238).
It is possible to obtain sufficient sodium chloride by consuming mainly animal products and meat consumption was likely the main source of sodium for many hunter-gatherer communities (Cordain et al. 2002). Hunting was probably the most common way in which humans obtained dietary salt before the introduction of domesticated animals. Even after the emergence of specialized herding, dietary sodium could still be obtained from blood (without killing the animal), milk, and urine. Pastoralist communities like the Maasai from Kenya are known to have consumed milk and blood from their livestock—all sources of dietary salt. Although this type of diet is difficult to trace, analysis of teeth and bones has provided evidence that during the 4th century bc, people in the Middle Nile Valley added salt in this manner to their diet (Alexander 1997). It is also possible that in many cases, hunter-gatherers harvested salt crystals that form on the low-lying ground near brine sources, as this would not have left any archaeological trace.
Explicit production and consumption of salt is often linked to the spread and adoption of agriculture, since prior to colonization, many historically documented hunter-gatherer societies did not add salt to food. There are accounts of communities who initially found its addition to food unappetizing, but quickly developed a taste thereafter. Studies among various groups in Australia’s Melville Islands, South Africa’s Kalahari Desert, and Argentina’s Tierra del Fuego indicate, however, that the use or aversion of salt is not related to the amount of agricultural products consumed (Kaunitz 1956). In addition, there is archaeological evidence that Jomon hunter-gatherer communities in Japan produced salt prior to the adoption of agriculture (Kawashima 2012, 2015). This does not mean that cultural practice and diet play an insignificant role in levels of salt use (e.g., Paque 1980). Saharan Bedouins, for example, do not add any salt to their food despite having readable access to it.
It is therefore also important to consider the value of salt in non-dietary terms. In many cultures, salt had clear symbolic meanings attached to it. For example, salt is sometimes associated with wit, wisdom, virility, fertility, barrenness, friendship, and food for supernatural spirits (Fregly 1980; Multhauf 1978; Potts 1984). In traditional Jewish communities, covenants were sealed with a salt exchange salt while Bedouins “will not attack a man whose salt they have eaten” (Fregly 1980, 8). In many Slavic countries, salt and bread are given to a new bride and groom to signal health and happiness (Fregly 1980). Salt also played an important religious role and formed part of offerings to Mesopotamian, Hebrew, Greek, and Roman gods (Adshead 1992; Fregly 1980; Potts 1984). In some parts of southern Africa, brine springs are sacred and associated with ancestral spirits. Here, taboos regulate the behaviors and actions of salt makers (Terblanche 1994).
Unprocessed Salt Sources
Unprocessed sources of salt are those sources where salt can be collected from the environment with no (or very little) further processing involved.
Where salt crystals form through solar evaporation on the land surface, salt can be scraped up and used as is. These crusts appear in dried up saltwater lakes and pans, on the soils around brine springs, and on the coast where lagoons form and dry out. These salt deposits were sometimes collected and consumed as a low-quality salt (Multhauf 1978, 22) or used as an animal feed supplement (e.g., Gouletquer 1975, 47).
In several places around the world, saline lakes have such a high mineral content that little processing is required. In the Peruvian Andes, for example, large quantities of salt form around the edges of small ponds as water levels recede (Parsons 2001). This salt was simply harvested as hard blocks and broken up with picks, shovels, and hoes. In Africa’s Rift Valley, several lakes have a salt content so high that salt crystals form on the water surface. When there is a substantial accumulation of crystals, these sink to the lake bed where they form salt beds that compact over time. These beds are “mined” by men wading into the water and breaking apart large chunks or slabs with metal rods (Fawcett 1973; Kirabira, Kasedde, and Semukuuttu 2013; Syahuka Muhindo 1989). At one of these, Lake Katwe (Uganda), salt makers construct woven grass barriers on the lake’s edge to trap salt crystals on the water surface as it is blown by the wind. The crystals wash up against the barriers in such abundance that they are scooped up by hand (Barrett-Gaines 2004; Kirabira et al. 2013; Morgan 1974; Syahuka Muhindo 1989). Residual moisture is simply squeezed out by hand and packaged and traded without any further processing (Fawcett 1973; Kirabira et al. 2013; Morgan 1974; Senior 1938).
Along the southern margins of the Sahara Desert, salt makers transform the landscape by excavating depressions in areas where the natural water table comes closest to the ground surface. The depressions can be up to 30 m wide and several meters deep, with wells dug into them (Sutton 1983, 17–18). The groundwater that percolates into these wells is often so highly concentrated that crystalline salt can be harvested directly from the well walls, dried in the sun, and cleaned for packaging and transport (Gouletquer 1975, 48; Lovejoy 1986, 54).
Sources of rock salt (halite) are comparably rare but where it does occur, these were extensively mined. In many cases, rock salt deposits occur near the surface and slabs can be excavated without further processing, which leaves comparably little trace. In Hallstat (Austria) and Wieliczka (Poland), deposits have been mined in extensive shafts and galleries dug along the halite seams (Harding 2013).
Coastal salt lagoons and salt marshes were also an important source of salt across the globe (Alexander 1997; Harding 2013; Sullivan 1981). In places such as coastal West Africa (Sutton 1983), the Mediterranean (Harding 2013), and the Caribbean (Sullivan 1981), evaporation was high enough for salt crystals to be collected from the edge of these features without any processing.
Making Salt from Brine
Ethnographic descriptions of unmechanized salt production from across the globe are tremendous sources of analogous information to archaeological salt production (e.g., Alexianu et al. 2015; Alexianu et al. 2011; Antonites 2013; Connah 1996; Good 1995; Gouletquer 1975; Gouletquer and Weller 2015; Parsons 2001, 2001). As a result, ethnographies are useful in the interpretation not only of salt production technology and method, but also in understanding the larger chaine operatoire and social context for salt production as well as changes in technology and production over time (e.g., Bednarczyk et al. 2015).
Where salt was not collected in a finished form from surface exposures or mined as rock salt, salt makers had to make crystalline salt by evaporating brine. Brine sources can be grouped as naturally occurring brine, brine from plants, and brine from saline earth.
Naturally Occurring Brine
Natural sources of brine rarely have a high enough salt content to be used without first concentrating it. Seawater, for example, has a salt content of 3.5 percent by weight, while inland lakes and springs typically range between 5 and 6 percent (Multhauf 1978, 7)—although there are some salt lakes with a content as high as 56 percent (Chiang 1976; Multhauf 1978; Pomeroy 1989). Raising the salt content of brine is known as graduation and can be achieved by washing salty materials such as seaweed, salty earth, or plants with the brine to increase its sodium concentration (Gouletquer and Weller 2015, 15). In temperate Europe from at least the 1500s (Multhauf 1978, 109), but possibly earlier (Bednarczyk et al. 2015), graduation was done by means of features known as graduation towers. These were wooden frameworks stuffed with plant materials such as bundles of brushwood (typically blackthorn) or straw. Brine was transported to the top of the towers from where it dripped down the bundles of twigs and branches. These towers could be 10 m high and hundreds of meters long, as at Ciechocinek and Inowrocław in Poland. This process increases natural evaporation rates, since it exposes a greater surface of the brine to air and wind and, when repeated over time, can significantly increase the concertation of brine (Harding 2013, 32). In warmer climates, brine from lagoons and the ocean was sometimes graduated in shallow ponds prior to further refinement.
Brine From Plants
Although salty leaves and roots can be used directly in cooking, brine was frequently made by combusting certain plants and rinsing the ashes off with water (e.g., Alexander 1997; Cardale-Schrimpff 2015; Davison 1993; Echeverri and Román-Jitdutjaaño 2011; Gouletquer 1975; Junod  1999; Mills 1989; Nenquin 1961; Schmeda-Hirschmann 1994; Stannus 1910). In New Guinea, there are also accounts of steeping non-saline plants in brine from salt springs before burning and using the ash (Gouletquer and Weller 2015; Kawashima 2012; Meggitt 1958). Making salt from vegetal sources is also recorded in ancient texts from Mesopotamia (Potts 1984), China, and Europe (Adshead 1992; McConkey and Breen 2017). While archaeologically difficult to trace, diatoms from marine plants could indicate the use of this method by salt makers from c. 2500–1250 bc in northern Japan (Kawashima 2012; Mori 1999).
Brine From Salt-Impregnated Earth
In much of the world, salt-rich soils occur around brine sources such as springs, salt pans, and marshes (e.g., Adshead 1992; Gouletquer and Weller 2015; Spann 2012). These soils are frequently more concentrated in salt than the water itself. Often, these soils are collected on a seasonal basis when water levels drop, leaving behind salt-enriched soils around the edge of the waterbodies.
In tropical east Africa, salt makers prepare “salt gardens” to maximize precipitation of salt on the ground surface through the capillary actions of salt ions from the uppermost few centimeters of underlying soil (Connah 1991, 1996, 1997). These gardens are small plots of cleared land on which loose soil is spread. Salt becomes concentrated in this loose layer during the day and is scraped up at the end of each day to prevent salt from leaching back into the ground when temperatures drop during the night. Each morning, the soil is re-spread and the process is repeated until the salt content of the soil is sufficiently high. When it reaches this stage, the salt-impregnated soil is placed in a leaching device where it is transformed to brine. Salt gardens can remain in use for a long time, are sometimes inherited, and are only abandoned when the yield falls and they are fallowed or if too many stones appear on the surface (Connah 1991, 1997).
To make brine, the saliferous soils are leached with water. This is typically done in a leaching device or strainer, of which many ethnographic and historic forms have been recorded. A common type of strainer is a woven, basket-like device recorded from Africa (Antonites 2013; Davison 1993; Gouletquer 1975, 1975; Lovejoy 1978; Sutton 1981;Sutton and Roberts 1968), South America (Cardale-Schrimpff 2015), and Mexico (Parsons 2001; Spann 2012; Williams 2002). Despite regional variations, the typical form is a funnel-shaped basket suspended on a wooden frame. The basket may be waterproofed with clay or plaster, leaving a small perforation at the bottom. Other examples of leaching devices include ceramic vessels with perforated bases (Connah, Kamuhangire, and Piper 1990; Davison 1993; Gouletquer 1975; Junod  1999), large perforated gourds (Morgan 1974; Sutton and Roberts 1968), and wooden troughs made from wood (Davison 1993) or clay (Good 1995; Mutema 1996; Nitta 1997). Regardless of the array of leaching devices, the process is largely similar: the device is filled with saliferous soils and then leached with water to produce brine, which is collected after it percolates through the filter.
Wherever soil is used as a basis for brine, production sites are characterized by the remains of the discarded leached-out soil. Continued over time, these often form mounds or large embankments and also contain other traces of the production process (Antonites 2013; Connah et al. 1990; Parsons 2001).
Reducing Brine to Crystalline Salt
Where salt is made from brine, energy is required to evaporate the water, either by means of solar evaporation or induced heat through boiling.
Solar evaporation of brine from the waters of coastal lagoons, inland salt lakes, and springs requires locales with a relatively low humidity and high temperatures. Evaporation takes place in shallow ponds defined by low earth walls and plastered with impermeable clay or lime to prevent seepage. In the coastal areas of Asia and Europe, salt makers used tidal forces to channel seawater into a series of large, interconnected evaporating pans (Adshead 1992; Multhauf 1978; Parsons 2001). Evaporation ponds were constructed in the shallows around salt lakes where water would be trapped as levels recede in the dry season (Syahuka Muhindo 1989). These systems can be fairly complex networks of interconnected, multistage decantation basins and an infrastructure of embankments, channels, dikes, and sluice gates. In other cases, solar evaporation in ponds was part of a process to clarify and concentrate brine prior to boiling it off by means of fire (e.g., Tsigarida 2015).
Solar energy alone is often not enough to efficiently produce salt, and brine is evaporated by means of heat application. Typically reducing brine to crystal form consists of simply placing containers filled with brine over a fire until the solution acquires the correct consistency. However, in many cases boiling was done in complex furnace features made from clay, masonry, and plastered frames (e.g., De Brisay 1975; Gouletquer 1975; Kondō 1975, 61; Nitta 1997).
Where ceramics are used for boiling, these inevitably break, since vessels are subject to great physical stress due to the caustic nature of the brine, as well as the heat from the fire and the accumulation of insoluble salts on the vessel surfaces (Parsons 2001, 213). As a result, boiling vessels are sometimes merely expendable molds for shaping cakes of hard salt, and these are then broken to remove the salt after a single use (Cardale-Schrimpff 2015; Gouletquer 1975; Lovejoy 1986).
In Europe, the massive deposits of coarse ceramic and unfired clay implements associated with boiling brine are known as briquetage. These special-purpose ceramics are especially associated with evaporation of seawater at coastal sites in France, Britain, Ireland, and the Low Countries, but also occur at inland European production sites (De Brisay 1975; Harding 2013; McConkey and Breen 2017). In Britain, briquetage mounds contain so much fired earth and clay that they are known as “red hills” (De Brisay 1975). Briquetage assemblages are characterized by the fragile, poorly fired, and roughly shaped vessels, which suggests expedient manufacturing.
However, boiling vessels were not always unique or specialist salt-making vessels. In some examples from sub-Saharan Africa, salt-making vessels were virtually indistinguishable from domestic ceramics typically found at settlements (Antonites 2013, 2016; Connah et al. 1990; Connah 1996; Fagan and Yellen 1968).
In all cases where ceramics were used, though, vessels inevitably broke during production, and the shards usually ended up on refuse mounds in the salt workshop with other debris, such as food remains, leached out soil, ash, and charcoal (Antonites 2013; Cardale-Schrimpff 2015; Connah 1997; Falkenhausen 2006; Gouletquer 1975; Muller 1984; Williams 2002). In places where there had been intensive and concentrated salt production, the landscape has been significantly altered, a prominent example being the accumulations in the Seille Valley of northeastern France. Here, 4,000,000 m3 of briquetage was deposited in places forming artificial hills up to 12 m high and 500 m in length (Olivier and Kovacik 2006).
As a result, fuel costs of brine boiling served as an inhibiting factor in salt making. For example, it was not until the advent of cheap peat and coal that commercial salt making became important in the face of high demand in places like northern Europe (Multhauf 1978). Boiling brine does have the benefit of separating sodium chloride from other less desirable forms of salt (Lovejoy 1986). Although boiling is a significantly faster method of reducing brine to crystalline salt, it does require adequate amounts of fuel (e.g., Connah 1991; Lovejoy 1986). The amount of fuel is directly related to the concentration of the brine, since a more concentrated solution requires less boiling (see Lovejoy 1986, 81; Parsons 2001, 214). As a result, salt makers sometimes had to concentrate the brine by solar evaporation prior to boiling, or where possible, relied solely on solar evaporation.
Ingots and Salt Cakes
In most ethnographic and historical sources, however, long-distance trade in salt was mostly conducted with hard salt cakes, cones, and cylinders between 1 kg and 50 kg. Sometimes salt slabs were purposely shaped into desired forms by sanding (e.g., Gouletquer and Weller 2015) or through ceramic or wooden molds of standard shapes and sizes (Birmingham 1999; Gouletquer 1975; Lovejoy 1986). Once a sufficient amount of water had been boiled down, it was removed from the heat when it reached a porridge-like consistency (Parsons 2001, 213). This damp salt was then formed into a cone shape by pouring the content onto a flat surface and forming a cone by ladling it with the hands. Sometimes the surface was further hardened through either low heat exposure that created a light seared surface to the cone (Antonites 2013; Terblanche 1994) or baking it in the sun (Gouletquer and Weller 2015). Once treated in this manner, the sealed and hardened outer surface provided adequate protection for transport and long-term storage. Granular salt was carried in containers such as baskets, skin, or bark-cloth bags (Parsons 2001, 219). For example, the use of leather bags by salt merchants for carrying granular salt over long distances is documented from the third millennium bc in southern Mesopotamia (Potts 1984, 255).
Because salt production was confined to specific locales where environment and geology allowed it, it was often an important trade item in the past. A significant impediment to the understanding of the salt trade is preservation. As a result, archaeologists infer trade from the organization of salt production activities(Antonites 2016; Weller 2002). Historical and ethnographic accounts, make it clear that some salt makers produced only what they required for their immediate household or local group needs, while in other cases, salt formed part of expansive exchange and tributary networks distributed over long distances.
In South America, North Africa, and Mesopotamia, mobile pastoralists played a key role in salt distribution networks (e.g., Parsons 2001; Potts 1984; Woldekiros 2019). This was likely due to the fact that key salt sources lay outside sedentary agricultural regions without local salt sources. In the well-documented case of the Saharan trade, mobile pastoralists formed an essential part of an intricate network of local-, medium-, and long-distance exchange systems that connected sub-Saharan Africa to the Mediterranean (Wilson 2012). Salt produced in the Sahara was exported to the south in exchange for gold and slaves, which were in turn traded northward to the Mediterranean for other goods (McDougall 1990; Wilson 2012). This trade existed since at least the early centuries ad, when Saharan salt sources likely formed part of the trade between the African Garamantes state and the Roman Empire (Wilson 2012; also see Woldekiros 2019). Significant intensification of trans-Saharan trade took place after the Arab conquest of North Africa (Insoll 2003). Subsequently, control over the salt resources in the Sahara became an important source of political power and revenue of Sahelian states from the Middle Ages onward.
The trade in salt was often closely tied to forms of political control, as several examples indicate. In 19th- and early 20th-century India, the British colonial authority monopolized salt production and trade through a system of severe taxation (Moxham 2001; Multhauf 1978, 18; Serajuddin 1978). This was also the case with the Chinese state, which controlled salt production and trade through a licensing system (Lattimore 1940, 43). In the Roman Empire, individuals were allowed to produce salt, but from the Middle Republic onward (c. 264–133 bc), the State had an exclusive monopoly on its trade, with large regions supplied by salt from major coastal and inland production centers (Saile 2015).
A focus on long-distance trade can obscure the important role of local small-scale production and short-distance trading. This scale of trade may actually have supplied the bulk of people’s salt needs in many cases (Alexander 1997; Tsigarida 2015). The long-distance trade in salt is linked to specific cases where its value was enhanced due to its status as a luxury item if it could not be produced locally or if there was increased demand for it (Tsigarida 2015).
The Study of Salt in the Past
Because salt can only be made at certain places, production sites are often locales of repeated human activity. In addition, the near universal desirability of salt means that salt production is often ideally suited to answer questions related to regional chronologies (e.g., Cardale-Schrimpff 2015; Connah 1997; Kawashima 2015). In both South and East Africa (Antonites 2013; Connah 1997; Evers 1973; Fagan 1963), for example, excavations of salt-making sites were key to establishing regional ceramic and cultural historical sequences, since most prehistoric societies here were mobile and very few stratified settlement sites exist (also see Cardale-Schrimpff 2015). As sites with deep chronological depth, salt-making sites are also some of the earliest identifiable Neolithic industries visible in the archaeological record, with sites in Japan (Kawashima 2012) and Europe (Guerra Doce and Von Lettow-Vorbeck 2016; Weller 2015).
Salt making as a specialist activity has been an area of considerable interest, since specialization is often regarded as a characteristic of social complexity and societal stratification and hierarchy (Arnold 1987; Brumfiel and Earle 1987; Clark 1995; Costin 1991, 2001; Flad and Hruby 2008; Rice 2009; Underhill 2002). Questions around specialization include discussions of investment of labor and infrastructure and the concentration of production and producers.
Increasing specialization of salt making is particularly pertinent in Asia, Europe, and Africa, where researchers have linked the control over salt production sites to the expansion of hierarchical political power. For example, in China’s eastern Sichuan Basin, small-scale producers made salt for consumers throughout the immediate region. However, changes in the scale of production, the organization of space, and burial practices led researchers to argue that control over salt resources came increasingly under elite control (Flad 2008, 2011). In addition, oracle bones at production sites imply that elites with privileged access to ritual knowledge controlled salt distribution and production (Flad 2008).
Similarly, elite interests in salt making are seen in Bronze Age Japan, where changes to production technology occur in step with an increasingly hierarchical political system. Early salt making in Japan used ceramic boiling vessels, which appeared to have been standard household vessels. Over time, salt-making vessels became more specialized and distinct from domestic ceramic ware. After the 11th century, metal boiling pans were used in much larger and more year-round specialist activities in specialized workshops. These changes are linked to the emergence of salt as a prestige item that local elites used to bolster their position in society (Kondō 1975).
The direct link between salt resources and local political authority is also illustrated in the lavish burials of the Hallstatt and Dürrnberg mines in Austria and the spatial link between bronze hoards and salt production sites in Transylvania (Harding 2013, 102–110). In addition, there seemed to be a spatial correlation between the distribution of salt springs and that of greenstone long alpine axes in Germany, suggesting that it featured in early trade links with communities in France (Guerra Doce and Von Lettow-Vorbeck 2016). At the Spanish salt-making site of Santioste and Molino Sanchón II, excavators have argued that symbolic and magical qualities of salt in Beaker period and Early Bronze Age society were exploited by elites for social control. This is seen in signs of feasting and intentional deposition of symbolically significant ceramics and rich graves in and around the salt production areas (Guerra-Doce et al. 2011).
Research on the organization of salt production characterizes production on a scale from full-time specialists to part-time salt makers for their own use (see Costin 1991; cf. Parsons 2001). In many cases, salt-making methods could only be conducted during certain parts of the year—typically during the dry season (cf. Parsons 2001). During the rainy season, shallow salt lakes, salt springs, and coastal lagoons are inundated with fresh water so that the crusts around the shore dissolve and disappear. Salt making evidently did not have to be a large-scale or full-time enterprise to supply the salt needs of a large community. For example, in the southern Maya lowlands during the Late Classic period (ad 600–900), autonomous specialized salt producers apparently supplied the required salt needs of the larger urbanized population centers (McKillop 2002). While there are arguments relating to the nature and scale of this trade (Kepecs 2003; Susan Kepecs 2004), the salient point is that household or small group-level salt production met the needs of large populations (Santley 2004, 219).
Many of the instances discussed in the ethnographic record—small scale, seasonal activity, multiple producer communities—do not fit the description of full-time or craft specialization. Instead, salt production sites are often nodes where a limited range of activities repeatedly took place over centuries and can therefore clearly be regarded as instances of site specialization (Muller 1984). This does not mean that it was in itself a small-scale endeavor, since in many cases enough salt had to be produced to supply large populations. At Uvinza in 19th-century Tanzania, for example, up to 20,000 people from various villages throughout the region came to make salt for a few days during the dry season (Sutton and Roberts 1968). Consequently, it is almost impossible to determine the output of salt making from the archaeological remains, since it could be the result of hundreds of small groups making salt over a short period or a smaller number of groups over a longer period. But even in the large-scale episode at Uvinza, the constituent production group remained small, making salt for their own use, and only over a few days.
Directly inferring changes in production output from the amount of salt-making debris or deposits is not straightforward and could be tied to technological changes. There is evidence to suggest that an increase in briquetage sites in Roman England is the result of an intensification of production linked to the emergence of new elites and new forms of political power, wealth accumulation, and prestige (Rodwell 1979). Formation of briqutage deposits in Europe ceased, however, when metal pans replaced ceramic boiling vessels (Guerra-Doce et al. 2011). Similarly, the apparent decline of salt production after the Late Mississippian Period (c. ad 1540) in the southeastern United States could be due to the adoption of a technological system that produced more subtle material remains rather than being purely a matter of lower salt production and use (Brown 1980).
Various sources of evidence present a picture of how salt is and has been produced in preindustrial societies. Despite the tremendous technological, organizational, and environmental variability that existed in traditional salt making and exchange, several patterns do emerge (cf. Parsons 2001, 234).
Crystalline salt is readily available in many areas from naturally formed deposits across the globe. While salt could be harvested without any further refinement at some places, in many cases, it had to be made from brine. Brine was reduced to crystalline salt either through solar evaporation or by means of heat-induced evaporation. Both methods can range from fairly simple technology with low labor and infrastructural investment to much more complex and expansive production systems.
Because salt was almost universally valued, control over this spatially restricted resource was often an important factor in regional politics. It also played an important role in local-, medium-, and long-distance trade routes between areas with abundant salt sources and those without. There is, however, an imperative in discerning between specialization production for trade by a small group of producers and production by multiple small-scale producers for their own use, since the archaeological remains of these two different production strategies may look very similar. As a result, archaeologists need to employ multiple lines of evidence in discerning the organization of production.
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