North Yorkshire Police are investigating after newly found Roman ruins in Scarborough were damaged.
The ruins, thought to be the first of their kind in the UK and possibly the entire ancient Roman Empire, were broken into at night on April 15.
Police have said that fencing and the land itself was damaged because of the break-in.
The find was discovered as part of excavation work for a new housing development, which has since been redesigned as a result of the significance of the finding.
A spokesman for Historic England said the Roman remains uncovered were more significant than anticipated with the complex including a circular central room, with several rooms leading off it, and a bathhouse.
A spokesperson for North Yorkshire Police said: "Our area’s rich heritage – dating back to when the Roman Empire was governed from York, and even earlier – is part of the reason why this is such a wonderful place to live and visit.
"Sadly, heritage crime can cause huge damage to assets of great historical interest. Indeed, the cost to communities of heritage crime is often immeasurable, resulting in the loss of artefacts to future generations.
"We need to work together to protect these sites so that others can continue to enjoy them for many years to come."
Historic England are set to recommend that the large complex of buildings found at the Eastfield site is protected as a nationally important scheduled monument.