The local tradition prevalent at the time of Charles Smith attributed it to one Griffith More, being a funerary chapel built by him or his family at their burial place.

"[2] However, according to lexicologist Pádraig Ó Siochfhradha (aka An Seabhac), the name does not refer to a foreign settlement but to a rocky headland (Gall-iorrus).

Charles Smith, who discovered the edifice in 1756, described the stone as "a brown free-stone, brought from the cliffs of the sea shore, which cuts readily and is very durable.

Antiquarian Charles Smith[11] is the originator of the claim that the building is an early Irish stone church although no historical information is available prior to 1756 regarding its use.

[12] In 1970, archaeologist Peter Harbison argued that the oratory might have been built as late as the 12th century for a number of reasons, mainly because the east window has a rounded top made of two carved stones (not a true arch).

[13] Harbison produced some evidence pointing to a later date and a different use: a letter by English traveller Richard Pococke who visited the oratory in 1758, two years after it was discovered by Charles Smith:[14] "Near this building they show a grave with a head at the cross of it and call it the tomb of the Giant; the tradition is that Griffith More was buried there, & as they call'd [it] a chapel, so probably it was built by him or his family at their burial place.

[17] Minor trial cuttings carried out at Gallarus in November 1970 yielded no finds or evidence of features or activity which might shed light on the period of construction and use of the oratory.