Pompey and Crassus conducted the levy for their campaigns in their provinces, which created discontent. Some of the plebeian tribunes instituted a suit nominally against Pompey's and Crassus' lieutenants that was actually aimed at them personally. The tribunes then tried to annul levies and rescind the vote for the proposed campaigns. Pompey was not perturbed because had already sent his lieutenants to Hispania. He had intended to let them deal with Hispania while he would gladly stay in Rome with the pretext that he had to stay there because he was the praefectus annonae. Crassus, on the other hand, needed his levy for his campaign against Parthia, and so he considered using force against the tribunes. The unarmed plebeian tribunes avoided a violent confrontation, but they did criticise him. While Crassus was offering the prayers, which were customary before war, they claimed bad omens. One of the tribunes tried to have Crassus arrested. However, the others objected and while they were arguing, Crassus left the city. He then headed for Syria and invaded Parthia. Plutarch thought that Crassus, the richest man in Rome, felt inferior to Pompey and Caesar only in military achievement and added a passion for glory to his greed. His achievements in the Battle of the Colline Gate (82 BC) and in the Third Servile War (71 BC) were now a fading memory. Plutarch also wrote that Caesar wrote to Crassus from Gaul, approving of his intentions and spurring him to war.