The Romans couldn't have destroyed Celtic anything, the Age of Saints is supposed to have occurred in the 5th, 6th, 7th or 8th century, i.e. the Dark Ages, according to "records".
there are Anglo Saxon churches still standing in various areas
Are there? Could you give some examples? Most of them seem to consist of fragments of 'Saxon stone' embedded in Norman structures and/or 'Anglo-Saxon crosses', usually discovered in the 19th century and which can't by their nature be accurately dated.
Just last week I was reading someone's blog about "the Early Christian Ecclesiastical site of Donaghmore", hugely important to the Irish because of its association with their patron saint, St Patrick himself. The present St Patrick's church at Donaghmore was built in the 19th century.
The place-name Donaghmore means ‘The Great Church’. Here in the 5th century AD St Patrick is thought to have established a church.
So no conclusive evidence there. "Thought to have" is a sure give-away.
The Donaghmore High Cross or St Mac Erc’s Cross is a highly sculptured granite ring-head cross which is 10 feet high and is thought to date from the 9th or 10th century AD. ...The ring-head probably came from another similar cross. It was re-erected at the S. side of St Patrick’s Church in 1891, but probably not in its original position.
The decorative carvings are remarkably un-Anglo-Saxon. Rather 'modern' one might think.
Depicted on the cross are several Biblical characters and scenes, and also panels with figures and decorative interlacing. Biblical characters and scenes on (W. Face) are: Noah’s Ark, Adam & Eve and Moses & David. The cross-head (W. Face) shows Christ’s crucifixion. He has long outstretched arms. At each side of Christ there are figures maybe of Stephaton and Longinus, two thieves and soldiers. An angel around Christ’s head. The (N. Face) depicts David & Goliath and interlacing. An angel on the cross-head. The (E. Face) has David or The Judgment of Solomon (David plays his lyre for Saul). Also figures, Moses smites water from the rock, David with the head of Goliath, David slaying the lion, The Last Judgment and St Paul with a bird or beast. S. Face has David and Solomon holding a child or other up-side down and St Paul or maybe St Anthony in the Desert.
https://thejournalofantiquities.com/201 ... n-ireland/
Checking the background a little more fully, I read that the place name is said to be derived from Latin (dominicum) so the 5th century church is presumably a Roman, not Celtic, site that pre-dates "St Patrick". More conclusively, no archaeological remains of St Patrick's church have been found
The name Donaghmore is derived from the Irish Domhnach Mór ‘large, great church’. The word domhnach is a borrowing from Latin dominicum and its presence in place-names is traditionally associated with the Patrician mission of the 5th century. The founding of Donaghmore is attributed to both St Mac Erca and St Patrick (Atkinson's Dromore 230) and according to a number of medieval sources St Mac Erca was bishop of Donaghmore in the mid-5th century .... No trace of his church remains, however, and the earliest archaeological evidence of an ecclesiastical site here is a stone cross in the graveyard of the church of Ireland. This cross dates from 11th-12th century (ASCD 291) and gave name to the townland of Tullynacross, now called Glebe.
http://www.placenamesni.org/resultdetai ... ntry=17817