OITA -- The Ao-no-Domon tunnel in Nakatsu, Oita Prefecture, said to have been built by a single person over some 30 years, has been closed to traffic since Nov. 30 due to a fallen rock. No one was injured, but a fence along the sidewalk was damaged.

The tunnel is said to have been chiseled out of the rock by Buddhist monk Zenkai between 1730 and 1763 so that travelers wouldn't have to use dangerous cliff-hugging tracks to get by the Kyoshuho Ridge. It has been designated a historical site by the prefectural government.

A tourist called police around 5:30 p.m. on Nov. 30 to report the fallen rock. The rock is approximately 2.5 meters high and 2 meters wide. The Nakatsu Municipal Government installed signboards and closed a roughly 750-meter section of a municipal road to traffic shortly after 7:30 p.m. that day.

City officials investigated the site on the morning of Dec. 2. As for the cause of the fall, it's reportedly possible that tree roots entered the weathered rock and pushed open a crack. The city will continue its investigation while keeping the site closed until the cause is identified and safety is confirmed.

(Japanese original by Nao Ishii, Oita Bureau)