The Ebola outbreak in West Africa is so out of control that governments there have revived a disease-fighting tactic not used in nearly a century: the “cordon sanitaire,” in which a line is drawn around the infected area and no one is allowed out.

Cordons, common in the medieval era of the Black Death, have not been seen since the border between Poland and Russia was closed in 1918 to stop typhus from spreading west. They have the potential to become brutal and inhumane. Centuries ago, in their most extreme form, everyone within the boundaries was left to die or survive, until the outbreak ended.

Plans for the new cordon were announced on Aug. 1 at an emergency meeting in Conakry, Guinea, of the Mano River Union, a regional association of Guinea, Sierra Leone and Liberia, the three countries hardest hit by Ebola, according to Agence France-Presse. The plan was to isolate a triangular area where the three countries meet, separated only by porous borders, and where 70 percent of the cases known at that time had been found.

Troops began closing internal roads in Liberia and Sierra Leone last week. The epidemic began in southern Guinea in December, but new cases there have slowed to a trickle. In the other two countries, the number of new cases is still rapidly rising. As of Monday, the region had seen 1,848 cases and 1,013 deaths, according to the World Health Organization, although many experts think that the real count is much higher because families in remote villages are avoiding hospitals and hiding victims.