The Polonnaruwa Period (1055 AD–1236 AD) was a significant era in Sri Lankan history, marked by remarkable achievements in irrigation, architecture, agriculture, and Buddhist culture. King Parakramabahu I transformed the kingdom through massive reservoirs and advanced water-management systems. The kingdom gradually declined due to internal power struggles, invasions from South India, and political instability. The invasion led by Kalinga Magha from South India around 1215 AD caused widespread destruction and contributed to the abandonment of Polonnaruwa as the royal capital, with political power shifting towards the southwest of Sri Lanka.