Gaius Julius Caesar was a Roman military and political leader and one of the most influential men in world history. He played a critical role in the transformation of the Roman Republic into the Roman Empire. Leading his legions across the Rubicon, Caesar began a civil war in 49 BC from which he became the undisputed master of the Roman world. After assuming control of government, he began extensive reforms of Roman society and government. He was proclaimed dictator for life, and he heavily centralised the bureaucracy of the Republic. These events provoked a hitherto friend of Caesar, Marcus Junius Brutus, and a group of other senators, to assassinate the dictator on the Ides of March (March 15) in 44 BC.