Abstract
Rome was famous because of its strong military force and it dominate the Mediterranean Sea. However, it was facing severe shortage of soldiers for a long time during 150 BCE. This problem had enormously effect on the Roman society and political life such as the appearance of slavery in Rome and the use of violence in Rome. The reasons why Rome had shortage f soldiers were related to its own military system and political system. The three great reformers, Tiberius Gracchus, Caius Gracchus and Caius Marius tried their best to solve the problem. Gracchus brothers failed but Marius succeed. Experiences we can learn from these reforms will also be mentioned.