The Anuradhapura Kingdom was one of the ancient kingdoms of Sri Lanka, established around the 4th century BCE. It served as the capital for over a millennium and is known for its advanced urban planning, irrigation systems, and impressive architecture. The kingdom played a crucial role in the spread of Buddhism in the region, with many stupas and monasteries built during this period. The kingdom reached its peak between the 3rd century BCE and the 10th century CE, becoming a center of trade and culture. Important sites include the Sri Maha Bodhi, a sacred fig tree, and the Ruwanwelisaya, a large stupa. The decline of the Anuradhapura Kingdom began in the 10th century, leading to the rise of the Polonnaruwa Kingdom.