The year of the consulship of Gaius Terentius Varro and Lucius Aemilius Paullus.

Okey thats not very helpful but that is how the romans were descibing years at the time. Referencing years in the context of rulers is a pretty common approach although things like "the 5th year of the reign of Seti II" are more common. While rome isn't too bad in this respect it makes constructing an accurate Egyptian chronology a pain in the neck since you have to work out how long each pharaoh was in charge for.

Back to the romans its not until over a century later that we see the first attempt to number dates in the form of ab urbe condita (from the founding of the City of rome). Battle of cannae would have been 537/8 A.U.C. but no one was using that system at the time.