The Ribat of Monastir is the finest surviving ribat in North Africa — a fortified Islamic monastery built in 796 AD on a rocky promontory above the sea. The ribat served a dual purpose: it was both a defensive military installation, from which watchmen scanned the sea for Byzantine and later Norman ships, and a place of religious retreat for scholars and fighters who believed that guarding the frontier of the Islamic world was itself an act of piety.
The building is remarkably well preserved. The central courtyard is surrounded by two storeys of monks' cells, and from the watch-tower at the corner there are excellent views across the old medina, the harbour, and out to sea. The interior houses a small museum of Islamic art with fine examples of calligraphy, ceramics, and woodwork from across North Africa. Entry is charged and includes access to the tower. It is the single most worthwhile sight in Monastir.