Just 600 wisent remain in the wild, nearly all of them here—or just half, depending on what’s meant by here. An iron curtain bisects this paradise, erected by the Soviets in 1980 along the border to thwart escapees to Poland’s renegade Solidarity movement. Although wolves dig under it, and roe deer and elk are believed to leap it, the herd of these largest of Europe’s mammals remains divided, and with it, its gene pool—divided and mortally diminished, some zoologists fear. Once, following World War I, bison from zoos were brought here to replenish a species nearly extirpated by hungry soldiers. Now, a remnant of a Cold War threatens them again.

Belarus, which well after communism’s collapse has yet to remove statues of Lenin, also shows no inclination to dismantle the fence, especially as Poland’s border is now the European Union’s. Although just 14 kilometers separate the two countries’ park headquarters, to see the Belovezhskaya Pushcha, as it is called in Belorusian, a foreign visitor must drive 100 miles south, take a train across the border to the city of Brest, submit to pointless interrogation, and hire a car to drive back north. Andrzej Bobiec’s Belorusian counterpart and fellow activist, Heorhi Kazulka, is a pale, sallow invertebrate biologist and former deputy director of Belarus’s side of the primeval forest. He was also fired by his own country’s park service, for challenging one of the latest park additions—a sawmill. He cannot risk being seen with Westerners. Inside the Brezhnev-era tenement where he lives at the forest’s edge, he apologetically offers visitors tea and discusses his dream of an international peace park where bison and moose would roam and breed freely.

The Pushcha’s colossal trees are the same as those in Poland; the same buttercups, lichens, and enormous red oak leaves; the same circling white-tailed eagles, heedless of the razor-wire barrier below.