After the Romans left Britain, the many towns set up by the Romans were abandoned and crumbled away as the new settler, Anglo-Saxons people went back to living in the countryside because they were farmers and build new kingdoms.
However, some Roman towns continued to exist and still exist today, which indicates the rich culture of the Romans.
Answer:
It all began when the Romans overthrew their Etruscan conquerors in 509 B.C.E. Centered north of Rome, the Etruscans had ruled over the Romans for hundreds of years. Once free, the Romans established a republic, a government in which citizens elected representatives to rule on their behalf.
Then the Great Roman Empire started its supports in its historic construction.
Source:
https://www.ushistory.org/civ/6a.asp
It attracted brilliant scholars from around the world