Rankot Vihara in Polonnaruwa, is it the largest stupa.

Rankot Vihara is indeed the largest stupa in Polonnaruwa, standing at an impressive 55 meters tall. However, it is slightly smaller than the colossal, ancient stupas found in Anuradhapura, like the Ruwanwelisaya, though it is still a massive and awe inspiring brick structure.