Inside Saint Patrick's Cathedral in Dublin

According to tradition St Patrick baptised several converts at a well  in what is now the park adjacent to the cathedral (the site is marked). To commemorate this event, a small wooden church was built. References to the well exist in many documents until the late sixteenth-century, but the site was eventually built upon. In 1901 the well was rediscovered and this ancient granite stone (marked with a Celtic cross) which covered the well was moved into the cathedral.  The parish church on this site was one of the four Celtic churches in Dublin and was knowns St Patrick's in Insula (on the island) as it was built on an island between two branches of the River Poddle which still flows under the cathedral

...Protection issued for four years for the preachers of the fabric of the church of St Patrick's Dublin, going through Ireland to beg alms for that fabric... John Comyn was succeeded as archbishop of Dublin by Henry of London in 1212, a close friend of King John's and one of those responsible for the building of Dublin Castle and the city walls. Henry was also one of the signatories of the Magna Carta in 1215. Henry made several additions to the original cathedral charter, creating the offices of dean, precentor, chancellor and treasurer, all of which were to be drawn from the chapter. Also all deans were to be elected by the chapter of canons from their own number. The cathedral chapter has retained this right to the present day. Henry is also responsible for beginning the process of  rebuilding the cathedral in the form in which we see it  today. The first surviving evidence of this is contained in an order from Henry III, dated 1225, allowing preachers to travel throughout Ireland collecting alms. The construction of the new church in the early English gothic style took about thirty years to complete. The building was re-dedicated under his successor Archbishop Luke in 1254 and the Lady Chapel was added by Archbishop Fulk de Saundford in 1270. The original tower and part of the west nave were destroyed by fire in 1362 but between this year and 1370 they were replaced by Archbishop Minot