Septimius Severus, 9 April 193 - 4 February 211 A.D.
This type probably refers to Severus' departure for his eastern campaign.
Silver denarius, RIC IV 106, RSC III 580, aVF, Rome mint, 3.18g, 17.0mm, 0°, 197 A.D.; obverse L SEPT SEV PERT AVG IMP VIIII, laureate head right; reverse PROFECTIO AVG, Septimius on horse pacing right, holding spear in right; scarce;
http://dl.dropbox.com/u/11761319/Sev%20cavallo.jpg