In 133 BC, Tiberius Sempronius Gracchus was elected in the college of tribunes in Rome. He was the spokesman of a small group nobiles who wanted land reform. Rome was experiencing increasing problems recruiting soldiers, which obviously meant a decline of power. To participate in the army, Romans had to have a certain fortune to finance their personal battle and maintenance costs. The easy solution to the recruiting problem would be to lower the property bounderies. But according to Tiberius this would mean that those less wealthy people would get in more financial trouble.
Tiberius and his supporters thought the number of economically healthy farmers should be increased. A natural grow of recruits would then be obvious. To increase the number of farmers, Tiberius Gracchus wanted to give a part of the state's land to proletarians.
The idea of handing public lands over to people without property was not a new one. Rome had done this before, especially when founding new colonies. In Tiberius' period most of the state's land was taken by large landowners. Although these actions were not legal, the Senate (mainly landowners) did clearly not approve of Tiberius' ideas.
Considering the to be expected resistance, Tiberius created a bill with a reasonable compensation for the land owners. He presented the proposal directly to the comitia tributa, the public assembly - without asking the Senate for the informal approval! Theoretically this had been a legal procedure since the lex Hortensia of 287, but it was not done. The Senate managed to convince another tribune (Marcus Octavius) to excercise his veto. Then Tiberius took another revolutionary step. He asked the comitia tributa to dismiss his colleague. Tiberius used the following argumentation: A tribune that had been appointed by the people to defend its interests, forfit his mandate automatically by turning against the will of the people. Ancient Greek democratic poleis were already familiar with this line of argumentation towards political officials.
Tiberius is not so much a revolutionary because of his ideas on land reform. His political procedures as such are much more important. By later generations, he was called the first popularis, a political leader who proposed directly to the public assembly, thereby ignoring the Senate. As said before, this was legal, but in Rome the mores (common and unwritten law) were often much more important than leges (written law).
When trying to get elected as tribunal for a second time (which was also according to leges and against mores), Tiberius Gracchus and 300 supporters were killed by a senatorial mob. In 123 his younger brother Gaius Gracchus continued Tiberius' reforms.