Parthia gets it (Orbis Romanum)

Timeline:  Orbum Romanum

June 5 44BCE Parthia Julius Caesar sets out to avenge the defeat of Crassus in 53 BCE where seven legions were lost. He moves from Syria to the mountainous regions of Armenia with four legions and 4,000 cavalry from Gaul. A large contingent of Roman engineers for operating ballistae and erecting defences are included. With his custumary speed Caesar arrives at the capital city of Ctesiphon before Parthian king Orodes II can intercept. The Romans start besieging the city while building defences against attempts to relieve it. Within a very short time they have built an incredible array of fortifications.

July 7 44BCE Ctesiphon The redoubtable Parthian archers are powerless against Roman defences. Every time they attack they are greeted with ballista volleys, not very accurate but steadily grinding down their numbers. Meanwhile siege engines bombard the walls. When the defenders of Ctesiphon become desperate Orodes II sends his heavily armored cataphracts into the Roman army. They dent the Roman lines but can't break them. Then everything seems to happen at once. The cataphracts are surrounded and slaughtered, Gaulish cavalry unexpectedly attacks the Parthian archers and the first cohort breaks through the walls of the city. No quarter is given as Parthian blood must flow to avenge Roman losses.