罗马大内战（前49年-前45年），又称为凯撒内战，罗马共和国最后的军事政治冲突之一。冲突在凯撒及其支持者（如平民派）和格奈乌斯·庞培及其支持者（罗马元老院和政治保守、社会传统的贵族派）之间开展。

在西班牙行省，意大利行省，罗马属希腊，伊利里亚，托勒密王国，阿非利加行省，进行了四年的战斗之后，凯撒在蒙达战役中击败了最后一批贵族派。在返回罗马之后，他获任为终身独裁官（Dictator perpetuo）。战争的影响是：罗马共和国的政治传统几乎完全毁灭，罗马开始向帝国转型。

The Great Roman Civil War (49–45 BC), also known as Caesar's Civil War, was one of the last politico-military conflicts in the Roman Republic before the establishment of the Roman Empire. It began as a series of political and military confrontations, between Julius Caesar (100–44 BC), his political supporters (broadly known as Populares), and his legions, against the Optimates (or Boni), the politically conservative and socially traditionalist faction of the Roman Senate, who were supported by Pompey (106–48 BC) and his legions.