André Geraque Kiffer 
Battle Of Carrhae, May 6th, 53 Bc [PDF ebook] 

The Crassus strategy, of course, should have been to avoid direct confrontation in the campaign. However, in the impossibility of reversing that decision, the consequent Operational Strategy should have been to guarantee bases of support (castra — fortified and supplied before proceeding), in which it could retract if it were caught at a disadvantage in the displacements, in this case to the village of Bathnae. The tactic will be to maintain the Orbis (large square) battle order, with light cavalry and infantry inside to counteract possible penetrations or to raid and dismantle the Parthians camel ‘train’ but fighting and retracting to Bathnae — prepared castra closest to the Euphrates River border (Zeugma locality).