According to some modern historians, Trajan might have busied himself during his stay on the Persian Gulf with ordering raids on the Parthian coasts, as well as probing into extending Roman suzerainty over the mountaineer tribes holding the passes across the Zagros Mountains into the Iranian plateau eastward, as well as establishing some sort of direct contact between Rome and the Kushan Empire. No attempt was made to expand into the Iranian Plateau itself, where the Roman army, with its relative weakness in cavalry, would have been at a disadvantage. Trajan left the Persian Gulf for Babylonwhere he intended to offer sacrifice to Alexander in the house where he had died in 323BC But a revolt led by Sanatruces, a nephew of the Parthian king Osroes I who had retained a cavalry force, possibly strengthened by the addition of Saka archers, imperilled Roman positions in Mesopotamia and Armenia. Trajan sought to deal with this by forsaking direct Roman rule in Parthia proper, at least partially. Trajan sent two armies towards Northern Mesopotamia: the first, under Lusius Quietus, recovered Nisibis and Edessa from the rebels, probably having King Abgarus deposed and killed in the process, with Quietus probably earning the right to receive the honors of a senator of praetorian rank (adlectus inter praetorios). The second army, however, under Appius Maximus Santra (probably a governor of Macedonia) was defeated and Santra killed. Later in 116, Trajan, with the assistance of Quietus and two other legates, Marcus Erucius Clarus and Tiberius Julius Alexander Julianus, defeated a Parthian army in a battle where Sanatruces was killed (possibly with the assistance of Osroes' son and Sanatruces' cousin, Parthamaspates, whom Trajan wooed successfully). After re-taking and burning Seleucia, Trajan then formally deposed Osroes, putting Parthamaspates on the throne as client ruler. This event was commemorated in a coin as the reduction of Parthia to client kingdom status: REX PARTHIS DATUS, "a king is given to the Parthians". That done, Trajan retreated north in order to retain what he could of the new provinces of Armeniawhere he had already accepted an armistice in exchange for surrendering part of the territory to Sanatruces' son Vologesesand Mesopotamia. It was at this point that Trajan's health started to fail him. The fortress city of Hatra, on the Tigris in his rear, continued to hold out against repeated Roman assaults. He was personally present at the siege, and it is