St. John's Cathedral is a Crusader church built in the 12th century, one of the better-preserved examples of Crusader ecclesiastical architecture in Lebanon. The building follows the standard Romanesque plan with a nave, two aisles, and an apse, and incorporates decorative elements that show both Western and local Byzantine influence. The open baptistery attached to the church is a distinctive element — a roofless open-air structure that was added in the medieval period and gives the church an unusual architectural profile.
The cathedral was converted to a mosque during the Mamluk period and underwent various modifications, but substantial original Crusader fabric survives. It sits within the walls of the archaeological site, which means access is included with the general site ticket. The interior is austere but well-preserved, and the play of light through the original window openings gives it a contemplative quality that contrasts with the more academic interest of the ruins around it.