Close view of the main arched entrance gate and flanking cylindrical defensive towers of Qaitbay Citadel (قلعة قايتباي) on the eastern tip of Pharos Island, Alexandria. The fortification, built in 1477 AD by Mamluk Sultan Al-Ashraf Qaitbay, is constructed from massive limestone blocks, many recycled from the ancient Lighthouse of Alexandria, one of the Seven Wonders of the Ancient World. The crenellated battlements, corbelled machicolations, and narrow arrow-slit windows visible in this image are characteristic examples of 15th-century Mamluk military architecture.