Lars Porsena came into conflict with Rome after the revolution which overthrew, in 510 BC, 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 (see Mucius, Horatius) 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 suggests 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. Porsena's tomb is described as having a 15 m high rectangular base with sides 90 m long. It was adorned by pyramids and massive bells. (Pliny the elder, Natural History, XXXVI, 19, 91ff.)
Lars Porsena's tomb, together with the rest of the city of Clusium, was razed to the ground in 89 BC by the Roman general Cornelius Sulla.
While the modern day Tuscan city of Chiusi has traditionally been considered the ancient site of Clusium, recent discoveries suggest that the location of the ancient city is closer to Florence. The archeological site of Gonfienti may turn out to be a part of ancient Clusium, believed to be the largest city in Italy before Rome.
Larousse stated in 1963/1965/1973 that "Roman myths ... frequently appear in the guise of history" (based on the work of Georges Dumézil). This would seem to support a most recent theory (yet to be officially "verified") that Lars Porsen(n)a may be a confounded Roman cognate of the Greek war god Ares which has cognate correspondences in other Indo-European branches. However it has been claimed that the name Lars comes from a word meaning "overlord". Significantly, that the Etruscan war god Laran had recently, previously been identified with Ares (again yet to be "verified"), noticing that y/j sometimes interchanges with l in Italic/Romance/Latin languages. The name Lars moreover seemingly bears a resemblance to Mars.