some 6,000 men. The Senate and Octavius had ordered Pompey Strabo – a commander in the northern theatre of the Social war – to return to Rome and defend the city with his army. Encamped outside the city, he was not prepared to commit for either side before treating with both of them. Cinna's forces then arrived and besieged the city. He led the main force opposite the Colline Gate, with two detachments under Sertorius and Marius on the north and south of the city, respectively. Strabo eventually sided with Octavius; the Senate, seeking support, also ordered Quintus Caecilius Metellus Pius, who was in the field against the Samnites, to make an honourable peace immediately and return to defend the city. When Metellus negotiated with the Samnites, they demanded citizenship for themselves and all those who had fled to them, release of all war prisoners, and non-reciprocal return of all plunder. Metellus and the Senate refused; Cinna and Marius, however, seized the opportunity and offered all the necessary concessions, gaining the Samnites as allies. After one of the military tribunes in Rome defected and opened the gates to the Janiculum, Cinna and Marius' forces moved to storm the city; they were, however, stopped by six cohorts from Strabo's army. Strabo, seeking to leverage his military forces into a second consulship, initiated secret negotiations with Cinna, but soon died of plague. Extending the siege, Cinna's forces fanned out across the countryside and successfully cut Rome's food supply. The Senate then sent envoys to Cinna to negotiate a truce. Initially put off by Cinna's demand that they address him as consul, the Senate acquiesced on this point after Merula abdicated his consulship. Extra-legal killings The envoys secured a promise from Cinna that he would not willingly kill anyone, but his ally Marius stood behind his chair, "grimly and ominously silent". Cinna then entered the city and promulgated a law recalling Marius and the Sullan exiles. A squadron of his cavalry, led by Gaius Marcius Censorinus killed the consul Octavius, who refused to flee. Censorinus then presented the consul's head to Cinna, "the first time a consul's head was so displayed". Cinna and Marius then moved to purge some of their political opponents: Gaius and Lucius Julius Caesar were killed without trial, along with Publius Licinius Crassus, and Marcus Antoinius. Merula – the recently-abdicated suffect consul – and Marius' old rival, Quintus Lutatius