Thousands of monastic tiles, regarded as the finest in Europe still in their original setting, have been unveiled for visitors after spending the winter under protective covers.

Every year English Heritage takes the precaution to prevent frost from damaging the historic surface of the mosaic at 12th-century Byland Abbey, near Coxwold.

And a study is now being carried out to try and find a more hi-tech solution, with electronic eyes installed around the ruins to monitor weather conditions.

Head custodian Ruth McIntyre said: "The tiles are one of the site's crowning glories and we get visitors from across the world coming to see them.

They tend to be at their best after a sharp shower, which really brings out the vibrant blues, greens and yellows."

Originally the tiles covered the entire floor of the Abbey church, founded by Cistercian monks in 1177, but are now mainly concentrated in its East end.

They were laid as early as the 12th century, possibly by craftsmen recruited for their expertise, and once numbered around 600,000 individual pieces.

The surviving tiles were re-discovered by archaeologists in the 1920s under soil and rubble, where they had lain undisturbed since the dissolution of the monasteries.

Originally they were shielded from winter's icy blast with bracken from the surrounding North York Moors _ a practise that was fortunately short-lived as the vegetation produced acid.