Complex sentence: As at Immae, the Palmyrene heavy cavalry (the "clibanarii") was superior to the Roman one, but dispersed in the pursuing of the Roman cavalry, and was massacred by the Roman infantry.
Split into simpler sentences: As at Immae, the Palmyrene heavy cavalry (the "clibanarii") was superior to the Roman equivalent. However, the clibanarii dispersed in the pursuit of the Roman cavalry, and were massacred by the Roman infantry.