Ancient Roman drain hidden beneath Bath is investigated

The investigation is due to last until December

Parts of an ancient underground drain, which takes Bath's famous hot spring water to the River Avon, are to be explored for the first time.

Engineers are surveying the Great Roman Drain, an ancient monument and fundamental part of the Roman Baths.

One branch runs from the King Spring, another from the Hetling Spring - they join under York Street before passing Bog Island and under Parade Gardens.

Previous nearby surveys have uncovered 34 gemstones and a mysterious tin mask.

The project is scheduled to finish on 9 December 2009.

The council regularly tests and monitors the city's spring waters, which includes ensuring that they flow uninterrupted into the River Avon through the Great Drain.

Previous surveys have ascertained that the condition of much of the drain is excellent for such an old structure.

Stephen Clews, the Roman Baths manager, on the drain investigation

However, below Bog Island the drain becomes so narrow that parts of it cannot be accessed.

Part of the drain appears to become blocked periodically, which leads to water backing up in the East Baths.

This increases the risk of flooding in the city following heavy rainfall, and possible damage to the fabric of the drain itself.

During the work, experts will be on hand to ensure nothing of archaeological value is lost.

Project manager Miles Barnes is responsible for the survey. He said: "This is an important and exciting project for Bath and North East Somerset Council.

"The Great Drain has played a crucial - but largely hidden - role in the life of the city for hundreds of years.

"It's crucial that we determine its condition so that it can continue to function as the Romans designed it.

"This project will enable us to complete the survey of the drain and be able to carry out repair or unblocking work in the future."