Answer:
It became the most important place of visit because Thomas a Becket was murdered there, and for his remembrance.
Explanation:
Just after the death of Thomas Becket, Pope Alexander elevated him to sainthood. Becket's shrine at Canterbury now became the most popular place in the country for pilgrims to visit.
When Becket was murdered, local people seemingly tried to acquire the pieces of his cloth soaked in blood.
A rumour started speculating that, once the people is touched by this cloth, they will be epilepsy, leprosy and blindness.
After sometime the monks at Canterbury Priory were selling small glass bottles of blood of Thomas Becket to visitors.
