Police have released CCTV footage of three people they would like to speak to in connection with damage to a drain pipe at St Albans Abbey.
Hertfordshire Constabulary said the offence occurred between 6pm on Saturday, August 2, and 7am on Sunday, August 3.
It is believed a fourth person was with the three pictured.
PC Ben Kirby said: "We are working closely with St Albans Cathedral to help safeguard this very important heritage site. Anyone who sees damage to this or any other building is asked to contact police immediately by calling 999."
Anyone with information on the identification of the people pictured or has information that may assist the investigation can telephone PC Kirby on 01727 796042 or the Herts Police non-emergency number 101. Alternatively, call Crimestoppers anonymously on 0800 555 111.