Arab Africa's boundary to the north is again a continental boundary, the Mediterranean Sea. This boundary begins in the west with the narrow Strait of Gibraltar, the thirteen kilometer wide channel that connects the Mediterranean with the Atlantic to the west, and separates Morocco from Spain to the north. East along the coast from Morocco are Algeria, Tunisia, and Libya, followed by Egypt, which forms the region's (and the continent's) northeastern corner. The coast turns briefly but sharply south at Tunisia, slopes more gently southeastward through the Libyan capital of Tripoli, and bumps north through Libya's second city, Benghazi, before turning straight east again through Egypt's second city, Alexandria, at the mouth of the Nile. Along with the spine of Italy to its north, Tunisia thus marks the junction of western and eastern Mediterranean, and a cultural transition as well: west of Egypt begins the region of the Arab World known as the Maghreb include (Libya, Tunisia, Algeria, Morocco and Mauritania).