Belvedere College in Dublin has appealed through the gardaí for help in finding the Chain Of Office of the Presidents of Past Pupils.
The chain, which was stolen in a weekend burglary, is valued at €20,000, and "it is of enormous historical and cultural value to the college", according to gardaí.
The burglary happened on Sunday afternoon between three and four p.m. The suspected thief is described as being in his late twenties, with dark shoulder-length hair. He was wearing a beige jacket, light blue jeans and a red t-shirt.
Anyone with information is asked to contact Fitzgibbon Street Garda Station at 6668400 or the Garda Confidential Line - 1-800-666-111.