The gold Solidus of 4.54 grams was introduced by Constantine the Great (306-337 CE) of Byzantine Empire and was the European standard for over a Millennium. The weight was adopted for Lanka's Kahavanu which was defined during that Era.
The coin was scanned at 600 dpi and displayed at 300 dpi.
In 2004 I was sent an image of a Byzantine Gold Solidus shown on lower panel which was claimed to have been found in Anuradhapura. It was worn and had been used as Jewellery as apparent from the crudely filled in hole. Ceylon Coins and Currency By H. W. Codrington does not mention any Byzantine coins found in Lanka. The coin on above panel is a Byzantine Gold Solidus of higher grade of same king purchased in 2004 from a Dealer in USA.