Overview of the Roman Triumph
The Roman Senate did not grant a triumph to a victorious general lightly. There was protocol to follow and and there were conditions to be met. Over time the conditions for a triumph changed. Exceptions had probably been made from the beginning, but basically, to earn a triumph, the victorious commander had to be the decisive victor in a campaign against non-Romans that cost relatively few Roman lives.
In the commander's triumphal procession, there would be captured prisoners, his own troops, the conscript fathers of the Senate, and the victorious commander (triumphator) in a golden chariot with a crown held over his head by a slave who would remind the triumphator that he was only mortal.
Upon his arrival at the Capitoline, the triumphator would(1) offer a sacrifice to Jupiter, (2) dismiss his army, and (3) begin the public feasts. It's because of #2 that Julius Caesar declined a triumph.
The Triumph Was a Great Honor
A triumph was a way to thank a victorious commander for his contributions to the state of Rome, which included plunder and conquered land. A triumph was so highly prized an honor that the Stoic Cato, who did not want Julius Caesar made consul [see Table of Roman Consuls], filibustered in the Senate to keep Julius Caesar from entering Rome to announce his candidacy for the consulate in time -- assuming that Julius Caesar would wait patiently for his triumph alongside his troops until the deadline for candidates had passed.
The Economy of the Roman Triumph
When a citizen of Rome ran for office he had to pay his own way. He could easily run into debt, as Julius Caesar did. Bribery and feeding one's clients some of whom accompanied the candidate on his daily rounds dressed in his specially treated cleaned, bleached, and chalked white (Latin: candidus -- whence, candidate) toga, was expensive. Julius Caesar also gained popular support in 65 B.C., when he was aedile, by putting on lavish public games. Unlike a campaign, a triumph was funded by the Senate, although afterwards, the triumphator would pay for feasts to feed the entire body of Roman citizens.
Rome's Safety vs. The Troops of the Triumphing General
Ordinarily, for the safety of Rome, a Roman army commander had to leave his command over his troops outside the city limits (beyond the pomerium). When a triumph was granted, the triumphator waited with the troops over whom he had command (imperium) beyond the pomerium until the day of the triumph and then led his (unarmed) army into the city of Rome. When Julius Caesar returned to Rome in 60 B.C., the Senate had granted him a triumph for his Spanish conquests, but Caesar had to wait until Cato stopped talking to receive that honor. Since Cato was filibustering and everyone knew it, Caesar realized that he would be too late to enter the city and get to the Forum Romanum to announce his candidacy for the office of consul. Only by becoming consul could Julius Caesar hope to be exempt from prosecution for illegal activities he had engaged in to earn the capital to repay his debts. For Caesar, the choice was clear. He left his troops beyond the pomerium, allied himself with Pompey against Cato, and ran for the office of consul.
Julius Caesar won the election for consul. Later he had other opportunities to earn triumphs. His hostile relationship with Cato did not improve. Although Caesar had not crossed the pomerium when he had earned a triumph for his Spanish conquests, he was moved to violate a Senate order to keep his army away from Rome when he wished to run for consul in 49. That was the momentous occasion when Julius Caesar led his army against his former ally Pompey and across the Rubicon.
Caesar Study Guide
Julius Caesar Triumph References(www.ualberta.ca/~csmackay/CLASS_366/Caesar.Consul.html) Cato
List of the Roman Consuls