In the absence of the technology of the use of concrete and the concept of an arch support, pillars for dwellings were chiseled from granite in the 2nd Century BC in Sri Lanka. Granite was available in plenty and was the raw material used. The picture shows some granite pillars at Sithulpawwa, Sri Lanka.
Worship of an image of Lord Buddha was a later developement. In the early years of Buddhism only objects signifying the presence of the Master ('sankhetha'), like a pair of feet, an umbrella, a whisk or an empty throne were used. This was in keeping with the philosophy of attaining Nibbana when 'nothing remains'.
This ancient site dating back to the 2nd Century BC is a mass of rock and trees. It has been used as a site of Buddhist meditation. The breezes from the ocean not far away give a tranquil atmosphere which owerwhelms one on a visit here. Click on the underlined web-link below to watch a video-clip of same:-