The Roman Empire was an Empire. A City of the Roman Empire was taken from Earth by a species called the Ribondastacria and frozen in time. Many years later it was unfrozen and became a space-faring country known as the Roman Empire for some centuries although humans in The solar system did not know of this. The actual Roman Empire collapsed in 395.
In 1011 BC there was an emperor called Admantar and thousands of years later he was alive again.