Colin Bord said this quote
“ Allegorical stories of saints battling with giants, monsters and demons may be interpreted as symbolizing the Christian's fight against paganism. At Bwlch Rhiwfelen (Denbigh) St Collen fought and killed a cannibal giantess, afterwards washing away the blood-stains in a well later known as Ffynnon Gollen. In Ireland, the tales of saints slaying giant serpents may have the same meaning; alternatively they (or some of them) may refer to early sightings of genuine water monsters. St Barry banished a serpent from a mountain into Lough Lagan (Roscommon), and a holy well sprang up where the saint's knee touched the ground. ”