A piece of stained glass window featuring a distinctive red cockerel that survived Henry VIII's dissolution of the monasteries and lay discarded but unbroken in rubble for centuries was today being unveiled.

English Heritage has returned the unique piece of 13th century stained glass window to Rievaulx Abbey, near Helmsley, North Yorkshire.

The fragile fragment, measuring ten centimetres square, has miraculously survived intact and is the most complete ever found at the 900-year-old ruins.

It is also the only one out of 8,500 glass pieces recovered from the site that depicts a complete animal.

It re-surfaced at English Heritage's Central Science Laboratory in Portsmouth as part of an ongoing programme to re-evaluate more than five million items in the national collection.

Andrew Morrison, English Heritage Senior Curator, said: ''This really is an exciting re-discovery. 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.'' The cockerel's first great escape came 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, incredibly staying intact.

Just after the first world war it saw sunlight once again. Archaeologist Sir Charles Peers used de-mobbed soldiers to clear Rievaulx's debris, which was up to five metres deep in places, and uncovered thousands of relics along the way.

However, records were often incomplete and after being lifted from the rubble the cockerel slipped the net and was soon entombed in an anonymous cardboard box for more than 80 years with few realising its importance.

For the Cistercian monks who built Rievaulx, the cockerel greeting the dawn every morning was symbolic of spiritual renewal and a new start. end