Greater Angkor was the product of massive and sustained landscape re-engineering over more than half a millennium. The urban complex had its ancestry in a landscape of small settlements in the late 1st millennium BCE and early centuries CE. Within that band of settlements skirting the great lake, the Tonle Sap, and along the rivers, two initial, urban centres, Ak Yum and Hariharalya, were added in the 7th and the 8th centuries CE. Mahendrapavarata was added on the Kulen plateau to the north. After Mahedrapavarta was abandoned, the conurbation of Greater Angkor was developed from the late 9th century by linking a new central area based around Phnom Bakheng to Ak Yum and Hariharalaya. The course of the proto Siem Reap river and the Puok and the Rolous rivers were altered, opening up a large expanse of land for widespread, residential clusters of occupation mounds, shrines and water tanks. By the 12th century CE Greater Angkor covered circa 1000 sq km of dispersed suburbs connected by roads embankments and canals, surrounding a central area which transformed during the 12th and 13th centuries. Integral to the development of Greater Angkor was the addition of large reservoirs (baray) and long canals and road embankments. The interconnected water management network was vastly expanded between the 9th and the 12th century. Within this urban complex, rulers added new, interconnected state temples, cumulatively concentrating towards the middle of Angkor. From the early 12th century, densification began in the central area of Angkor, around a road grid and numerous small ponds and house mounds. By the early 14th century Greater Angkor was being adversely affected by regional political and social changes and by severe climate instability. The urban area rapidly declined into the 15th century and after the 16th century transformed into a linear configuration of housing and Buddhist shrines from the former central urban area down to Phnom Krom on the edge of the lake.