Sandakada Pahana, also known as Moonstone, is a unique feature of the architecture of ancient Sri Lanka.[1][2][3] It is an elaborately carved semi-circular stone slab, usually placed at the bottom of staircases and entrances. First seen in the latter stage of the Anuradhapura period, the sandakada pahana evolved through the Polonnaruwa, Gampola and Kandyan period. According to historians, the sandakada pahana symbolizes the cycle of Samsāra in Buddhism.

Known in Sinhalese as sandakada pahana, it is roughly translated into English as moonstone. The name is based on its shape and design.[2] The ancient chronicle Mahavamsa and Pali chronicle such as the Samantapasadika refer to the sandakada pahana as patika.[4]

https://en.wikipedia.org/wiki/Sandakada_pahana