It also talks about the conquests of the 'horse peoples', first under the Assyrians, then the Achaemenids, Parthians and Sassanids; then in the 7th century the Arabs conquer a lot of territory, followed by the Mongols under Genghis Khan and finally the last of the horse peoples under a Mongol named Tamerlane, who unleashes massive carnage and destruction.
It is a quadrifrons trumphal arch, surmounted by an unusual octagonal cupola,and was erected (entirely in marble) by Gaius Calpurnius Celsus, quinquennial duumvir of the city, to commemorate the victories of Lucius Verus, junior colleague and adoptive brother of the Emperor Marcus Aurelius, over the Parthians in the Roman–Parthian War of 161–66.
According to this inscription, the statue was carved in 139 BC on the occasion of a conquest for Seleucid Greeks (under Demetrius II Nicator) against the Parthians (under Mithridates I of Parthia), though the Seleucids were later defeated and driven from the region.
In Roman times, Harran was known as Carrhae, and was the location of the Battle of Carrhae in 53 BCE, in which the Parthians, commanded by general Surena, defeated a large Roman army under the command of Crassus, who was killed.
After Julius Caesar was murdered in 44 BCE, Quintus Labienus, a Roman republican general and ambassador to the Parthians, sided with Brutus and Cassius in the Liberators' civil war; after their defeat Labienus joined the Parthians and assisted them in invading Roman territories in 40 BCE.
After Brutus and Cassius fled east to Macedonia and were defeated there in the Battle of Philippi by Caesar's imperialist successors (the Second Triumvirate, particularly Mark Antony and Caesar's heir Octavian, the future emperor Augustus), Labienus joined the Parthians.