While Christianity was long established as the religion of the Britons at the time of the Anglo-Saxon invasion, Christian Britons made little progress in converting the newcomers from their native paganism. Consequently, in 597, Pope Gregory I sent the prior of the Abbey of St Andrew's (later canonised as Augustine of Canterbury) from Rome to evangelise the Angles. This event is known as the Gregorian mission and is the date the Church of England generally marks as the beginning of its formal history. With the help of Christians already residing in Kent, Augustine established his church at Canterbury, the capital of the Kingdom of Kent, and became the first in the series of archbishops of Canterbury in 598. A later archbishop, the Greek Theodore of Tarsus, also contributed to the organisation of Christianity in England. The Church of England has been in continuous existence since the days of St Augustine, with the archbishop of Canterbury as its episcopal head. Despite the various disruptions of the Reformation and the English Civil War, the Church of England considers itself to be the same church which was more formally organised by Augustine.