One of the most famous ancient cities built over 2100 years ago is Petra, located in modern-day Jordan. Established as early as the 4th century BCE as the capital of the Nabataean Kingdom, Petra was at its peak of power and architectural splendor roughly 2,100 years ago (around the 1st century BCE). Known as the "Rose City" due to the color of the stone from which it is carved, its most iconic structure, Al-Khazneh (The Treasury), was likely constructed during this era. Other cities that fit this timeline include Rome, which was a bustling Republic-turned-Empire 2,100 years ago, and Xi'an in China, which served as the capital for the Han Dynasty. These cities represent the pinnacle of ancient urban planning, featuring sophisticated water management systems and monumental stone architecture that has survived for over two millennia.