The reasons for these four executions remain obscure. Official recognition of Hadrian as legitimate heir may have come too late to dissuade other potential claimants. Hadrian's greatest rivals were Trajan's closest friends, the most experienced and senior members of the imperial council; any of them might have been a legitimate competitor for the imperial office ("capaces imperii"); and any of them might have supported Trajan's expansionist policies, which Hadrian intended to change. One of their number was Aulus Cornelius Palma who as a former conqueror of Arabia Nabatea would have retained a stake in the East. The "Historia Augusta" describes Palma and a third executed senator, Lucius Publilius Celsus (consul for the second time in 113), as Hadrian's personal enemies, who had spoken in public against him. The fourth was Gaius Avidius Nigrinus, an ex-consul, intellectual, friend of Pliny the Younger and (briefly) Governor of Dacia at the start of Hadrian's reign. He was probably Hadrian's chief rival for the throne; a senator of highest rank, breeding, and connections; according to the "Historia Augusta", Hadrian had considered making Nigrinus his heir apparent, before deciding to get rid of him.