Also known as the library dagoba, the Potgul Vihara in the far south of Polonnaruwa is an unusual structure. A thick-walled, hollow, dagoba-like building, it is thought to have been used to store sacred books. It’s effectively a circular gedige, and four smaller solid dagobas arranged around this central dome to form the popular Sinhalese quincunx arrangement of five objects in the shape of a rectangle (one at each corner and one in the middle).