Humanitarian corridors are meant to evacuate civilians in war. But they can be dangerous.

Evacuees from Mariupol, Ukraine, are seen March 16 at a shopping center on the outskirts of Zaporizhzhia, which is now a registration center for displaced people. (Emre Caylak/AFP/Getty Images)

As shelling from Russian forces rains down on major Ukrainian cities, thousands of people are sheltering in subway stations, libraries and theaters while others try to escape.

To facilitate their evacuation and the arrival of aid into hard-hit areas, Ukrainian and Russian officials have periodically agreed to establish humanitarian corridors — with mixed results. While Ukraine has said that tens of thousands of people have used these routes, it has also accused Russia of repeatedly attacking protected areas.

Safe passageways during times of conflict date back to at least shortly before World War II, when 10,000 children were transported out of Nazi-controlled countries on trains, boats and planes called “kindertransports.” In 1949, the Geneva Conventions established protocols to ensure civilians have access to critical goods such as medicine during war.

But history shows that humanitarian corridors offer no guarantees. Time and again, civilians have been hit while trying to escape along a route that was supposed to be safe. Even when they work, they often aren’t a solution for the most vulnerable.

“It’s basically a desperate measure to get civilians out of a place where they’re either out of supplies or they’re in constant danger,” said Crystal Wells, a spokeswoman for the International Committee of the Red Cross. “But this often means that there’s a lot of people who are left behind. What happens if you’re bedridden, if you’re old, if you don’t really have an option to get out?”