If you stand on the shore of a briny lagoon near the mouth of Belize’s Monkey River, you won’t see many signs that ancient industry once flourished here. Today, all that’s left are dozens of submerged clusters of wooden posts—some now overgrown with mangroves, all long buried in silt—and artifacts like pottery and stone tools. But a thousand years ago, the community now submerged beneath the lagoon’s placid surface may have supplied salt and dried fish to a network of Maya cities.

As airborne laser studies reveal how complex Maya trade networks were hundreds of years ago, microscopic analysis of Maya stone tools suggests that salt cakes and dried fish may have been among the most important goods carried on those trade routes.

Before Etsy, there were Maya marketplaces

A thousand years ago, the people who lived near the lagoon’s shores would have spent the four-month dry season—when water in the lagoon evaporated, leaving behind an especially salty brine—heating brine in clay pots over fires and boiling away the water until a cake of salt was left in the bottom of the pot. Each household here would have maintained its own salt kitchen, and many would have lived adjacent to their work (at least during the dry season) or in the nearby community of Wild Cane Cay.

This kind of cottage industry was typical of Maya working life by the Late Classic period. From crops to pottery, obsidian to salt, households would use what they needed and sell the rest in markets. Don’t think of that household surplus as small potatoes: a single salt kitchen, run by a single household, could have turned out six tons of salt in a single season.

At the modern Maya community of Sacapulas in Guatemala, two people working in a single salt kitchen can produce 56.7kg of salt a day. If ancient Maya households were that productive, one of them could produce enough salt to meet the needs of nearly 7,000 people every day. And dozens of such households set up shop by the shores of the Payne’s Creek lagoon. Trading networks connected those individual households to the wider Maya economy.

“Surplus household products were taken to marketplaces within large cities such as Caracol and Tikal and marketplaces at other communities,” wrote archaeologists Heather McKillop of Louisiana State University and Kazuo Aoyama of Ibaraki University in Japan. A depiction of a marketplace on a wall at Calakmul includes a salt vendor, labeled with the Maya glyph for salt, and chemical analysis of a set of human remains from the inland city of Tikal suggests that the individuals there consumed salt brought from the coast.

Not exactly fresh, local seafood

A closer look at stone tools from underwater sites at Payne’s Creek suggests that these household salt kitchens were also turning out salt-dried fish and meat for transport to marketplaces in inland cities. McKillop and Aoyama examined the edges of 20 chert blades from the site under a microscope. On 16 of the tools, the microscopic striations and polishing on the stone matched the sorts of wear caused by cutting fish or meat.

Six others had wear that suggested the tools had been used to scrape hides, which could have been mammal, reptile, or fish. That suggests that, in addition to producing salt, people at Payne’s Creek also salted fish. Like the salt cakes, dried fish would probably have been both a household necessity and a valuable trade commodity.

Further inland in southern Belize, a city called Lubaantan thrived at around the same time as Wild Cane Cay and the salt works at Payne’s Creek. Archaeologists have unearthed animal remains there—both discarded meals and ritual items—and 39 percent of those remains are marine fish like jack, grouper, and snook, which still swim in the waters near Payne’s Creek.

Most of the pottery at Payne’s Creek that wasn’t used for salt-boiling is in the same style as that found at Lubaantan. That combination suggests that people from the coast traded fish to people at Lubaantan, perhaps in exchange for pottery and other goods. A canoe and wooden paddles found at Wild Cane Cay suggest that traders could have traveled up the river to Lubaantan.

Fish bones have turned up in middens and as ritual items at other inland cities in Maya territory, as well, suggesting a strong link between coastal and inland markets. If McKillop and Aoyama are correct, the Maya join a long list of civilizations that relied on trade in salted fish to provide a storable, high-calorie food source in times of famine. Dried fish was a key commodity in medieval Europe, where it helped build the vast trade network of the Vikings, as well as in imperial China, the Philippines, and ancient Rome.

PNAS, 2018. DOI: 10.1073/pnas.1803639115 (About DOIs).