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When Julius Caesar crossed the Rubicon in 49 BC, he expressed disrespect to the Roman Senate and started the war against it. Today, the meaning of crossing the Rubicon refers to making a challenging decision that can have unpredictable consequences.

Explanation:

Before that war, there existed the Roman Republic, and Caesar was one of its generals. Together with Crassus and Pompey, Caesar created the First Triumvirate to manage their nation. However, their establishment failed to be overall beneficial for the Roman Republic because of disagreement among the triumvirs.

Thus, Crassus’ death marked the beginning of the crisis in the country. At that time, Caesar dealt with conquering Gaul and controlling the new territory. As for Pompey, however, he gathered the support of the Senate and became the sole consul of the Republic. That situation was not attractive for Julius Caesar, who also had ambitions to be a ruler of the nation. That state of affairs denoted that the alliance between Pompey and Caesar came to an end.

Thus, the Senate ordered Caesar to disband his army and come to Rome. However, he refused to follow that requirement and decided to get power with the help of his warriors. In 49 BC, he approached the Rubicon, the border of the Roman Republic. There, he paused to assess whether it was the right decision to start a civil war. “The die is cast” were the words of Caesar crossing the Rubicon.

Even though the decision was difficult, it resulted in significant benefits for Caesar. He managed to win in the civil war and become a dictator of the Roman Empire. Thus, crossing the tiny river resulted in significant consequences for Julius Caesar and his nation.