The ancient structure built as a fortress for the Persian King Xerxes was the Gates of All nations, known as the "Gate of Xerxes," located at Persepolis. Built during the 5th century BCE, this magnificent structure served as a grand entrance to the ceremonial capital of the Achaemenid Empire. Persepolis itself was a symbol of the empire’s power and architectural prowess, showcasing tastefully decorated halls, reliefs, and monumental staircases. The site held immense cultural and historical significance, representing the grandeur of the Persian Empire and its contributions to architecture and art that influenced later civilizations.