Memorials to mark devout person's remains outside (10)

'memorials' is the definition.
(tombstone is a kind of memorial)

'to mark devout person's remains outside' is the wordplay.
I cannot really see how this works, but
'to' is present in the answer.
'mark' could be 'm' and 'm' is found within the answer.
'person's' could be 'ones' ('one' can mean an unspecified person) and 'ones' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?