Blenheim Palace's lost ballroom, theatre and chambers seen for the first time in 250 years

The lower rooms of Sir John Vanbrugh’s famous Grand Bridge at Blenheim Palace, Oxfordshire, have recently emerged, albeit temporarily, from murky underwater depths for the first time in 250 years. Capability Brown flooded them in the 1760s when he created the 40-acre lake, forming what Lord Randolph Churchill (father of Winston) dubbed ‘the finest view in England’.

Findings in the ‘habitable viaduct’, which contains a ballroom, theatre and various other rooms complete with fireplaces, include 18^th-century graffiti, sunken boats used for reed cutting in the 1950s, original plasterwork, stairways and what is possibly a cooking range.

The work is part of a £12 million, 10-year restoration project of the landscape and lakes; some 400,000 tonnes of silt must be removed to protect the Grade I-listed, 120m-long Grand Bridge, which has a 30-metre-wide central arch flanked by smaller arches and four corner towers.

Blenheim, now a UNESCO World Heritage Site, was built as a gift for Gen John Churchill, 1^st Duke of Marlborough, in honour of his victory over the French in the War of the Spanish Succession, particularly at the Battle of Blenheim (1704), from Queen Anne and the nation. As the ancestral home of the Dukes of Marlborough, it is the birthplace of Sir Winston Churchill and, in the 19^th century, was saved from ruin by the 9^th Duke’s famously unhappy marriage to American railroad heiress Consuelo Vanderbilt.

In the English Baroque style, it is often called Vanbrugh’s masterpiece, an architect whose ambitions plans and escalating costs caused Sarah, the 1st Duchess of Marlborough, so much annoyance that he was later banned from setting foot on the estate.

Originally, Vanbrugh’s Bridge contained 33 chambers; one large room was described sarcastically by the Duchess in 1716 as ‘for a ball if there were occasion’ and others included a bathing place and a boat house.

‘The dredging of Queen’s Pool and the repairs to the Grand Bridge are not only our greatest challenge to date but also mark some of the most ambitious stonework and dredging projects ever attempted in the UK,’ says Blenheim’s Head of Estates Roy Cox.

‘If all goes according to schedule this initial investigation will enable us to draw up detailed plans for the main work, which is likely to begin towards the end of this year and into 2020.’

Five things you didn't know about Blenheim Palace, from helping with royal adulterers to its unique role in equal rights

Blenheim Palace, the Duke and Duchess of Marlborough's Oxfordshire home, is one of the most famous country houses on the

Cumberland Lodge: The 17th century marvel 'a thousand times more agreeable than Blenheim'

This year, a remarkable educational foundation in a spectacular parkland setting celebrates its 70th anniversary. John Goodall considers the history

Will 1,000 new homes make or break the town of Woodstock?

Forget peace and love: the town of Woodstock (the British version, naturally) is set to become the nucleus of more

6 famous rhetorical devices used by Winston Churchill

We reveal 6 of his most famous flourishes.