These ruins, exactly halfway between Phnom Penh and Siem Reap, are even older than those at Angkor. They are all that remain of the 7th-century Sambor Prei Kuk, the capital of Zhen La, a loose federation of city-states. The ruins, which are free and open to the public at all times, are near the Stung Sen River, 35 km (22 mi) northeast of the provincial town of Kampong.