Probably identical with Rājāyatana-
The cetiya was perhaps erected in honour of the Rājāyatana tree, which was brought by Samiddhisumana from Jetavana when he came with the Buddha to Sri Lanka (See Mhv.i.52, 57 f).
It is said (DA.iii.899) that when the Buddha’s religion disappears, all the relics of the Buddha in Sri Lanka will gather together at the Mahācetiya, proceed from there to the Rājāyatana-