This is what remains of a post-classic Khmer stone bridge, located between Angkor Thom and the East Baray, which formerly spanned the Siem Reap River. Water flowed through the corbelled arches of the bridge, whose stones were reused from several post-Bayon temples.
According to Jacques Dumarcay ("Khmer Hydraulics," Millennium of Glory, pp.93-100), this and other bridges in post-classic Angkor were built as irrigation dams, substituting for the by-then silted-up and useless barays. The arches of the bridge would be blocked in order to fill the dam. Unfortunately, its engineering proved to be inadequate. The bridge's west abutment gave way, releasing its retained water in a flood. The river changed course as a result, diverting around the bridge and into its present channel.