Complex sentence: The Byzantines were divided into two corps, one either side of the river, and caught the Seljuq army in an ambush when it had partially crossed over the bridge and destroyed it as a fighting force.
Split into simpler sentences: The Byzantines were divided into two corps, one concealed on each side of the river. They caught the Seljuq army in an ambush when it had partially crossed over the bridge, destroying it as a fighting force.