195 AD., Septimius Severus, Rome mint, Denarius, RIC 63.

Septimius Severus, Rome mint, Jan. - March 195 AD.,
Denarius (17-19 mm / 3,85 g),
Obv.: L SEPT SEV PERT - AVG I[MP] V , laureate head of Septimius Severus right.
Rev.: PART ARAB PART ADIAB / COS II PP , trophy of arms with two bound captives in Phrygian caps, their hands tied behind their backs, seated back to back on their shields.
RIC IV, I, 98, 63 (scarce) ; BMC 40, 121 ; Coh. 365 ; RSC III 365 .

This coin refers to a contemporary event, Septimius' successful campaign against the Parthian vassals who had supported Pescennius Niger in the civil war - Severus´ victory over the `Arabians and Adiabenians´.
In his campaign Septimius' first victory was in Mesopotamia ca. Dec. 194 AD.
After arrival of news of the victory in Rome, whereupon Senate votes Septimius the titles PART ARAB PART ADIAB (ca. Jan. 195). These titles are placed on his coins.
The news of the senatorial action gets back to Septimius in Mesopotamia, whereupon he rejects the title Parthicus, as he didn't want to offend the Parthians. So dropped Parthicus from the titles voted him by the Senate for his first victory over the Parthian vassals. This coin with PART was struck soon after the award of the titles, but before Septimius' reaction was known in Rome.
The news of Septimius' rejection of Parthicus returns to Rome, titles on coins shortened to just ARAB ADIAB (ca. March 195). In the course of IMP V PART was then dropped and the titles became merely ARAB ADIAB. "Lest he offend the Parthians", as his vita says, (ca. Feb. 195).
(based on Curtis Clay´s data about these issues)