MOSCOW — Resembling an aircraft hangar, a giant arched shelter was slid into place over the Chernobyl nuclear disaster site in Ukraine on Tuesday. The shelter, the world’s largest land-based moving structure, is a feat of engineering decades in conception and years in the making.

The arch, which was first designed more than two decades ago and has been under construction since 2010, covers the deteriorating steel and concrete sarcophagus that had been hastily built after a botched test at the power plant led to an explosion and fire that sent plumes of radioactive ash across Europe 30 years ago.