Answer:
According to a blog maintained by the History Department at Harvard University, Rome was a republic for 450 years until it became an empire under Julius Caesar.
The British Museum has determined that the fall of the Roman Empire took place by the fifth century AD
These two senteces above are used in the passage to show credibility.
This is because they make reference to two institutional authorities that have credibility and prestige in academic history, and the cultural world: the History Department at Harvard, and the British Museum.
In other words, the Harvard and the British Museum are the sources of the passage.
