A UNIQUE piece of 13th-century stained glass depicting a striking red cockerel has been returned to Rievaulx Abbey.

English Heritage discovered the fragile fragment in an old cardboard box at its Central Science Laboratory, in Portsmouth, during an ongoing programme to re-evaluate more than five million items in the national collection.

The piece, which is 10 cm square, is the most complete ever found at the 900-year-old site and is also the only one out of 8,500 glass pieces recovered that depicts a complete animal.

"This really is an exciting rediscovery," said Andrew Morrison, English Heritage senior curator.

"We've never found anything as good as this fragment before bearing a complete animal motif.

"It appears it came from the east end of the Abbey church, which was built to house the shrine of Rievaulx's most famous abbot St Aelred."

For the Cistercian monks who built Rievaulx the cockerel greeting the dawn every morning was symbolic of spiritual renewal and a new start. Set within the great eastern window, the cockerel would have been lit up by beams from the rising sun.

The cockerel was first taken from Rievaulx Abbey, near Helmsley, in 1538 when Henry VIII looted the nation's abbeys, with the best quality glass being sent to London and lesser grades sold locally or melted. Experts believe the king's men discarded the cockerel as rubbish and it joined more than 50,000 tonnes of masonry, soil and rubble that accumulated over the next four centuries.

It was dug up after the First World War by archaeologist Sir Charles Peers who used demobbed soldiers to clear debris at Rievaulx.

Thousands of relics were uncovered, but records were incomplete and after being lifted from the rubble the cockerel was placed in an cardboard box for more than 80 years before its importance was realised.

"The sheer number of relics uncovered by Sir Charles meant that it was inevitable many would go unrecognised for their importance," said Mr Morrison. "Record keeping was at times patchy. That makes our programme to reappraise the entire English Heritage collection an important, but also very daunting task."

John Lax, head custodian at Rievaulx, said: "It's also possible that the supposedly austere Cistercians simply wanted something whimsical around the borders of the window to lighten its appearance. Whatever the motivation, it is a very high-quality piece of work that would have been painted by a professional craftsman. It's a miracle it has survived and we hope to have it on display to the public soon."

Updated: 11:03 Wednesday, October 08, 2003