3Rourke, Grellan D., and Jenny White Marshall. "The drystone oratories of western Kerry," in Marshall, Jenny White, Claire Walsh, Grellan D. Rourke, E. V. Murray, and Finbar McCormick. Illaunloughan Island: an Early Medieval Monastery in County Kerry. Bray, Co. Wicklow: Wordwell, 2005. 119-120.
The authors acknowledge that the stone oratories cannot accurately be dated. But they present structural evidence that Gallarus "...represents the final phase of the development of the drystone oratory." Citing the carefully chosen and worked stones that provide the maximum contact area for stability, and the fact that the lateral walls, unlike the gable walls, rise straight up for a meter before they begin corbelling inward, the authors conclude that these modifications are the primary reason why Gallarus is the only such structure still completely intact.