Vandals have spray-painted graffiti on a historic fountain, walls and flagstones at Linlithgow Palace.
Historic Environment Scotland said it was “heartbroken and outraged” after the centuries-old site in West Lothian was “badly defaced”.
The palace, famous as the birthplace of Mary Queen of Scots, has been closed to visitors but was due to reopen this summer after masonry repair work.
The ornate fountain within the palace, built by James V in 1538, was also physically damaged.
Historic Environment Scotland said its experts were assessing the vandalism.
“We are heartbroken and outraged by recent vandalism at Linlithgow Palace,” a spokesperson said.
“Our expert colleagues are working hard to address this damage before the Palace reopens, but we want to be very clear that any vandalism of historic buildings, including graffiti, is a heritage crime.
“It can cause irreparable damage to historic sites, divert resources from other essential maintenance work and cause us to lose pieces of our past forever.
“Police Scotland are investigating the incident. If you have information that could help, please report it on 101, or via Crimestoppers on 0800 555 111 or www.crimestoppers-uk.org”