Many are familiar with the great battles of the Roman Empire, the ones which decided whether Rome would rule the known world or not. What many are not as familiar with are the great battles which decided the fate of the once mighty Roman Republic.
The Battle of Philippi, perhaps the most decisive battle in Roman history. The forces of the Second Triumvirate against the forces of the Liberators Army headed by Marcus Brutus and Cassius. It was perhaps the largest clash of arms in Roman history, however it is often overlooked as a non important event of antiquity. However I think an AH timeline in such a scenario would be most interesting.
By this time Octavian and Mark Antony had joined together in an alliance known as the Second Triumvirate. With their united armies they descended on Greece in hopes of taking Brutus and Cassius by surprise and effectively destroy them, which they did. Modern estimates put Antony and Octavian's army at a little over 100,000 men while the army of Brutus and Cassius numbered just under 100,000 men. The battle was hard fought and was heavy in casualties but eventually Octavian and Antony overwhelmed their enemies. What if though...what if against the odds Brutus and Cassius prevailed and Octavian and Antony defeated on the battlefield in Greece, and not just a defeat but a decisive blow. Let us assume Antony and Octavian suffer a defeat on par with the one suffered by Brutus and Cassius in OTL. They are forced to flee the battlefield in hopes of fighting again another day. So what if Brutus and Cassius and the forces of the Republic had indeed prevailed over those who would eventually turn Rome into what we know as the "empire"?