It covers the period from 52 BC - 44 BC -- from the end of Julius Caesar's campaigns in Gaul to ... (I won't ruin the ending, but it's pretty common knowledge how the first season ends.) Main characters include Caesar, Pompey the Great, Marc Antony, Octavian, Cato, Cicero, Brutus, etc. Also two "commoner" soldiers who happen to get mixed up in these world-shaking events.
Supposedly there will be a second and final season, covering the period 44 BC - 30 BC.
Guy