Churches, monasteries and early Celtic churches were built across Ireland in the centuries after Patrick's death. High crosses in Ardboe and Donaghmore, County Tyrone, Tynan in County Armagh and Kilbroney in County Down demonstrate ninth and tenth stone depictions of biblical scenes. There are monastery ruins in Nendrum, Inch Abbey and Grey Abbey. Nendrum was built in the fifth century. The sites of some present day churches and cathedrals were chosen as links to places of earlier Christian worship. Saint Patrick's Church of Ireland Cathedral in Armagh stands where Patrick's original church was built. The church in Saul is on the same site as Patrick's first church in Ireland.
But the mission was more than the construction of churches and crosses. The real legacy is realised in the success of the evangelising Irish Church. This early celtic Church flourished with many monks and priests leaving Ireland to begin missions in Europe. In the first two hundred and fifty years after Patrick's death, around five hundred Irish saints were recognized. These missionaries established monasteries in Scotland, England, Switzerland, France, Germany and as far south as Italy.
Patrick's two contemporary disciples, Saint Tassach and Saint Olcan, are associated with counties Down and Antrim. Saint Tassach was a skilled craftsman who made croziers, patens and chalices. Patrick appointed Tassach as Bishop of Raholp. Tassach gave Patrick the Last Rites before his death. The deathbed scene is poignantly captured in stained glass windows at Saint Tassach's Church and Saint Patrick's Church, Saul. Saint Olcan was ordained by Patrick in Dunseverick Castle and founded a monastery in Armoy. Near the ruins of Cranfield Church, Saint Olcan is believed to have blessed a well which people still visit for healing cures. Saint Comgall founded Bangor Abbey in Bangor, County Down, where he was abbot to three thousand monks. He instructed the monks who went to France and also accompanied Colmcille on a mission to Inverness. Saint Colmcille who studied under Saint Finnian, founded monasteries in Londonderry, Durrow and Kells. As penance for a battle fought in his name, he went into exile in Iona. There he founded a monastery and later evangelised the Picts. Saint Laiserien, who was also known as Saint Molaise, was a sixth century hermit monk who established a monastery on Devenish Island in County Fermanagh.
During these centuries, Ireland was a centre of Christian learning and training for priests and monks. Highly stylised, ornate books of the gospels were created by monks in Armagh, Kells and Durrow. The Book of Armagh includes seventh century biographies by Tírechán and Muirchu of Saint Patrick.
These apostles of Saint Patrick went out from Ireland and brought the Christian faith to Europe. Monasteries, churches and precious books of the gospels are reminders of an Irish Christian legacy which spread across Europe. With the advent of the invading, destructive Vikings, many of the missions to Europe ceased. When the Vikings reached Ireland in 795, they desecreated churches, burned religious books and pillaged monasteries. Viking rule ended at the Battle of Clontarf in 1014. With the Norman invasion in 1169, the conquerors built new monasteries and abbeys to rival earlier centres of Christian worship. Monasteries were built by Normans at Inch Abbey and Grey Abbey in County Down. These ruins are close to Strangford Lough where Patrick first landed in 432.