Why is Canterbury called Canterbury?

In the 4th and 5th century when the Romans were here, Canterbury was known as Durovernum which means Stronghold. 

The Colosseum which stood in Canterbury which is believed to of been twice the size of the one in Rome.

After the Romans left, the residents used less than 10% of the stone to build as what we now know as the city wall. The rest remains buried under the centre of Canterbury. 

Canterbury at the time was such a lawless place at the time that you had to bury anything of value outside of Canterbury because you wouldn't be leaving with it. The population back then was approx 3,000 now it is 43,000 not including all the students we have living in the City. 

Back then when you came into Durovernum you had to canter in because of the mud, the road quality was not great. You would have to bury your goods outside of Durovernum. 

The English wanted an English name for the city that's why they chose Canterbury.