DJENNE, Mali (AP) — Thousands of Malians carrying buckets and jugs of mud joined the annual replastering of the world’s largest mud-brick building this weekend, a key ritual that maintains the integrity of the Great Mosque of Djenne in the center of the country.

The building has been on UNESCO’s World Heritage in Danger list since 2016. The mosque and surrounding town, a historical center of Islamic learning, have been threatened by conflict between Islamist rebels, government forces and other groups.

Djenne’s mosque requires a new layer of mud each year before the start of the rainy season in June, or the building will fall into disrepair. The replastering event once drew tens of thousands of tourists each year. As with the rest of Mali, Djenne’s tourism industry has all but completely disappeared.

Amadou Ampate Cisse, a Djenne resident taking part in the event, told The Associated Press: “The plastering of the mosque is a symbol of peace. The poor, the rich, everyone is here for this activity. We will continue this tradition from generation to generation. We will pass it on to our children and they in turn will do the same.”