The next day, Poinar knelt head down over a trench in area 2000, trying to excavate a jaw with teeth protruding from the wall of the pit. The team hadn’t yet gotten radiocarbon dates from this trench, but they thought it might be from the 14th century, a time of devastating infections including the Black Death, which killed half of Europe from 1348 to 1350. The teeth glistened in the dirt wall, but the jaw was firmly embedded. “I’ve been drooling over them for 4 days,” Poinar said.
Earlier that week, he had explained why. He gave a presentation in the church and flashed a slide about a news story about a plague-infected squirrel that closed campgrounds near Los Angeles. “Killer squirrels are coming!” he joked.
But it’s no joke to ask if killer strains of plague could return. In 2011, Poinar was part of a team that gathered ancient DNA from people who died in London between 1348 to 1349, apparently of plague. The scientists identified the cause of the Black Death as the bacterium Yersinia pestis, rather than anthrax or a mix of pathogens, as some had suspected. This ancient strain was almost identical to a Y. pestis strain that still circulates in small rodents in the southwestern United States, Africa, and Asia. But today, Y. pestis, although still deadly, infects only about 1000 to 3000 people annually and is transmitted slowly from person to person.
Why is this Y. pestis strain so much less virulent today, and why does it only rarely move from rodents to humans? Poinar is one of several geneticists in a neck-to-neck race to find out. They’re trying to learn when and why the Black Death strain jumped from rodents to humans, and what made it spread so rapidly. Was it mutations in the genome of Y. pestis or changes in the susceptibility of animal or human hosts—or both?
“If we study humans before, during, and after the plague, we should see how the human genome responded to these repeated outbreaks and the response in bacteria,” Poinar says.
That’s why he is seeking the Black Death in Badia Pozzeveri, where cases were recorded in 1348 before the epidemic reached northern Europe. He’ll compare that strain—newly arrived from Asia—with that of the London victims to see if the plague evolved as it tore through Europe. He also can see if plague victims suffered from TB or other infections, to test the idea that 14th century people harbored so many pathogens that they were more susceptible to plague.
Another theory behind the deadliness of plague is that it was hard for anyone in Europe to survive that terrible century. Before the plague hit, the continent had been pounded by bad weather, failing crops, famine, and war. Torrential rains in 1315 and 1316 flooded crops and caused the Great Famine. The Little Ice Age had begun, triggering frigid winters that destroyed more crops. In England, between 1348 and 1375, life expectancy at birth was only 17 years, according to parish records. Overall health, as shown by seven indicators in teeth and bones, plummeted to an all-time low in the 14th century, according to a study of 17,250 individuals from 100 locations in Europe by Ohio State economic historian Richard Steckel, Larsen, and their colleagues in the Global History of Health Project (Science, 1 May 2009, p. 588).
Disease may even have influenced the outcome of battles among the Italian city-states, which came right to the doorstep of the church at Pozzeveri. In September 1325, Florence’s commander Ramon de Cardona camped at the abbey with most of his 3000 cavalry and 15,000 infantry. The nobles moved into the monastery itself, while the troops probably camped in a field west of the church, near what was then a large lake and swamp. Many got sick.
That may be why Cardona made a move that still puzzles historians: He lingered at Badia Pozzeveri for two long weeks while his rival, the legendary Castruccio Castracani from Lucca, recruited reinforcements. Castracani had far fewer troops at first. But by the time Cardona advanced on 23 September, Castracani’s army outnumbered the Florentines, many of whom retreated before the battle had even begun. It was a rout, and Castracani became a hero whose military victories were immortalized by Machiavelli.
Just what sickened Cardona’s men? Fornaciari suspects malaria because they complained of mala ariae, or bad air. He convinced Poinar to test for that disease, too. “One of our hopes is to discover if malaria is present in the medieval period,” Fornaciari says, because it is not clear when the illness first reached Tuscany.
Another hope is to find the remains of those who died in that famous battle, because relatively few groups of soldiers killed in war have been found in Europe, Larsen says. Three spearheads have turned up so far in area 4000. Human remains would provide the first good physical “record of injuries from the kinds of weapons available in 1325,” Larsen says. “They were doing some really horrible things to each other. They had this square hammer-headed mace for bashing in skulls.”