Christopher Salisbury, an amateur archaeologist from Plumtree in Nottinghamshire, spotted huge timbers in the quarry, near Castle Donington, and called in professional colleagues to conduct an excavation.
Now, after four weeks digging, the substantial remains of a great medieval timber bridge have emerged. Dating work on the timbers - conducted by the University of Nottingham tree ring dating laboratory - show that the bridge was constructed in the late 11th century, at about the time of the Domesday Book.
About 25 per cent of the bridge's timbers have survived, including Britain's earliest known large-scale examples of sophisticated carpentry. The structure is 30 to 40 yards long, 10ft wide and was built using at least eight different types of lap and butt joints.
Archaeologists were surprised by the discovery - because old maps gave no hint of a bridge being sited where the gravel pit now operates.
However, examination of geological evidence shows that up to 700 years ago the river Trent ran through the site and the bridge would have been an important crossing point. It may have formed part of the medieval track that became the A6 Derby-to- London road, now located one and a half miles to the west.
By the 13th century the Trent had changed its course and a new bridge - this time made of stone - was built 50 yards to the south- west. This too has been located and excavated.
The river had changed its course yet again by the 17th century and now runs a quarter of a mile from the rediscovered 11th and 13th-century bridges.
The discovery of the 11th-century timber bridge sheds vital new light on the beginnings of English carpentry. It is one of the earliest examples of the woodworking tradition that blossomed into the timber-frame architectural style of the 13th to 17th centuries, for which Tudor England became so famous.
A Leicestershire County Council archaeological team, led by Patrick Clay and Susan Ripper, has now unearthed the late 11th- century timber bridge and a possible predecessor dating from perhaps a decade earlier.
Some 70 timbers have been found so far, including groups of timbers making up three or possibly four of the original bridge piers.
There are also the remains of a trestle structure which was either built in conjunction with the piers or as part of another late 11th-century bridge, constructed on the same site. The bridge or bridges seem to have collapsed during one or more severe floods.
Some archaeologists say the carpentry and architecture of the bridge represent 'a crucial moment in British building history'. It combines the 'earthfast' - based in the ground - building technology of Anglo-Saxon England with the timber-frame technology which became commonplace a century later.
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