altar

壇 is composed of 土 (earth) and 亶 (true, real). 亶 is composed of 㐭 (granary) and 旦 (dawn), conveying the image of a granary built on flat, open land. 土 represents the terrain or ground, therefore 壇 is used to indicate a raised or protruding section of the ground. This meaning later extended to refer to an elevated platform used for performing sacrificial rites or ceremonies.