Located at Roluos south of Preah Ko, Bakong was built in late ninth century (881) under the reign of Indravarman I.

The temple-mountain style architecture was erected in tiers within a strict geometric matrix, a style recognizable in the later Angkor Wat.

Bakong was the center of Hariharalaya, which was the capital at the time, and is speculated to have been the state temple of the King.

Bakong consists of a moat enclosing an east-facing rectangular complex, at the center of which is a multi-tiered central sanctuary, similar to the temples that followed it for much of the next 400 years.

The sanctuary is surrounded by several towers, which probably memorable for close members of the royal court.