jan 1, 509 BC - Rome becomes a republic

Description:

The Roman Republic started with the fall of the monarchy and made way for the implementation of the constitution of Rome and the twelve tables. This was important because previously there was not a clear declaration of the laws of Rome and it allowed for the citizens and plebians to understand the rules and protect themselves from the abusive power of the patricians.

Source: https://en.wikipedia.org/wiki/Roman_Republic#Foundation_(509_BC)

Added to timeline:

Date: