Beneath the Royal Mint Court, diagonally across the street from the Tower of London, lie 1,800 mute witnesses to the foresight of the city fathers in the year 1348. Recognizing that the Black Death then scourging Europe would inevitably reach London, the authorities prepared a special cemetery in East Smithfield, outside the city walls, to receive the bodies of the stricken.

By autumn, the plague arrived. Within two years, a third or so of London’s citizens had died, a proportion similar to that elsewhere in Europe. The East Smithfield cemetery held 2,400 of the victims, whose bodies were stacked five deep.

The agent of the Black Death is assumed to be Yersinia pestis, the microbe that causes bubonic plague today. But the epidemiology was strikingly different from that of modern outbreaks. Modern plague is carried by fleas and spreads no faster than the rats that carry them can travel. The Black Death seems to have spread directly from one person to another.

Victims sometimes emitted a deathly stench, which is not true of plague victims today. And the Black Death felled at least 30 percent of those it inflicted, whereas a modern plague in India that struck Bombay in 1904, before the advent of antibiotics, killed only 3 percent of its victims.