509 BC -- 27 BC
The Roman Republic was the phase of the ancient Roman civilization characterized by a republican form of government; a period which began with the overthrow of the Roman monarchy, c. 510 BC, and lasted over 450 years until its subversion, through a series of civil wars, into the Principate form of government and the Imperial period.

Rome also saw its territory expand during this period, from central Italy to the entire Mediterranean world. During the first two centuries, Rome expanded to the point of dominating Italy. During the next century, Rome grew to dominate North Africa, Iberia, Greece, and what is now southern France. During the last two centuries of the Roman Republic, Rome grew to dominate the rest of modern France, as well as much of the east. By this point, however, its republican political machinery was finally crushed under the weight of imperialism.

Many of Rome's structures can still be seen throughout Europe and the Republic's doctrines on government have been refined abroad by modern countries and organizations.

27 BC -- AD 476/1453
The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean.The term is used to describe the Roman state during and after the time of the first emperor, Augustus.

In the late 3rd century AD, Diocletian established the practice of dividing authority between four co-emperors, in order to better secure the vast territory. During the following decades the empire was often divided along an East/West axis. After the death of Theodosius I in 395 it was divided for the last time.

The Western Roman Empire collapsed in 476 as Romulus Augustus was forced to abdicate by Odoacer.The Eastern Roman or Byzantine Empire endured until 1453 with the death of Constantine XI and the capture of Constantinople by the Ottoman Turks led by Mehmed II.

The Roman Empire is long dead, yet the reminiscences of its history, methodology, values and lifestyle, still lay around. The enduring Roman influence is reflected pervasively in contemporary language, literature, legal codes, government, architecture, engineering, medicine, sports, arts, etc. Much of it is so deeply inbedded that we barely notice our debt to ancient Rome. Consider language, for example. Fewer and fewer people today claim to know Latin — and yet, go back to the first sentence in this paragraph. If we removed all the words drawn directly from Latin, that sentence would read; "The."