Final answer:
After Caesar, Rome transitioned from a Republic to an imperial form of government, which is essentially a monarchy with an emperor at its head, starting with Augustus Caesar.
Step-by-step explanation:
After Caesar, Rome was ruled by a form of government known as an empire, which is a type of monarchy that encompasses a wider swath of territory. This shift occurred when Augustus Caesar, Julius Caesar's adoptive heir, established the Roman Empire after Julius Caesar's assassination and the end of the Roman Republic. Though the Senate remained a fixture in Roman political culture, its power fluctuated, and it was often overshadowed by the emperor's authority.