Lars Porsena (sometimes spelled Lars Porsenna) was an Etruscan king known for his war against the city of Rome. He ruled over the city of Clevsin , called Clusium by the Romans (and known as Chiusi in modern times). There are no established dates for his rule, but Roman sources often place it at around 500 BC.

Lars Porsena came into conflict with Rome after the revolution which overthrew Lucius Tarquinius Superbus, the last King of Rome. The deposed monarch, whose family was of Etruscan origin, appealed to Lars Porsena for assistance in suppressing the new Roman Republic, and Lars Porsena agreed to help.

At this point, however, there is divergence in the histories. According to most mainstream Roman accounts, including those of Livy, Lars Porsena arrived at Rome, but was sufficiently impressed by Roman bravery in defending the city that he chose to make peace. Other accounts, however, suggest that Lars Porsena actually succeeded in capturing the city, and that the Etruscans were only driven out some time afterwards. None of the accounts suggest that Lucius Tarquinius Superbus was returned to the throne, however, perhaps indicating that if Lars Porsena did indeed capture Rome, he did so with the intent of controlling it himself, not restoring the former dynasty.

According to most accounts, Lars Porsena was buried in an elaborate tomb in (or under) the city he ruled. The tomb is believed to have survived until at least the 1st century BC, but is believed to have been destroyed at some point. It is sometimes suggested that some of the catacombs under modern Chiusi might have been part of Lars Porsena's tomb, but this is not thought likely by most archaeologists.