Al-Mahdiyya is a coastal city in present-day Tunisia, 200 kilometers (124 miles) south of Tunis, founded by the first Fatimid caliph, ʿUbayd Allāh al-Mahdī (r. 909–934), to be his capital in place of Qayrawan. The establishment of a capital on the coast represented a singular break with Islamic tradition, which since the time of the conquests in the seventh century was to build new urban administrative centers inland away from the Byzantine Sea (as the Mediterranean was called). Al-Mahdiyya did not replace Qayrawan as the metro…