A 2000 year old lead ingot mined by the Romans shortly after they conquered Britain is expected to fetch up to £12,000 when it goes under the hammer this month.

The 154lb ingot, known as a 'pig', was mined by Romans in North Yorkshire, and would have been due to be made into piping of waterproof lining for roofs. Silver could also be extracted from it.

The Romans, who ran well organised mining operations in Britain and also produced silver and gold after invading the country in AD43.

Dating from AD81, the 11 stone pig bears a raised inscription on the top reading 'Imperatore Caesare Domitiano Augusto Consule Septimum’ - a reference to the Emperor Domitians seventh consulate.

Measuring 58.5cm by 10.5cm by 13.5cm, it has the word 'Brig' on the side - showing it came from the territory of the British Brigantes tribe, who had fallen under Roman rule.

The pig was discovered accidentally in 1731 in peat on Hawshaw Moor, which was famous in antiquity for its lead mines. A second, similar ingot was also found.

The first recorded document about the pig dates from 1768 and states it was the property of Sir Thomas Ingilby, if Ripley Castle, North Yorkshire.

The Ripley Castle guidebook records that the pig was kept on a radiator shelf.

It is expected to fetch between £8,000 and £10,000 when it goes to auction at the Bonhams auction of Antiquities and Tribal Art on April 26.

A Bonhams spokesman said: "The lead `pig’ or ingot is a massively tangible remnant of the occupation of these islands and its exploitation by the Romans."