If you go down to the cellar today ...

Two ancient tablets from Assyrian palaces have turned up in a Herefordshire castle.

Imogen Hervey-Bathurst has a vivid imagination. She's 12 years old, lives in a gothic castle and likes a treasure hunt. But even she never expected to find hidden treasure on her own doorstep.

Imogen has spent hours exploring the maze of cellars underneath Eastnor Castle, near Ledbury in Herefordshire, but neither she nor her parents, James and Sarah Hervey-Bathurst, had any idea there was anything priceless down there. Then, earlier this summer, as they rummaged through piles of accumulated junk on a wet Sunday afternoon, they found something remarkable. Two Assyrian tablets or wall panels, worth millions and around 2,700 years old.

The stone panels appeared to have been stored haphazardly in the cellars by the Hervey-Bathursts' ancestors in the late 1800s. Yet there was no record of their whereabouts, or even of their existence, anywhere in estate documents. "This cellar has been a bit of a dumping ground. For generations, everything has just been put down there," Sarah Hervey-Bathurst explains. "It's taken us 10 years to get around to sorting it out. After all, there are 97 rooms here."

The pair of alabaster, or gypsum, slabs were spotted propped up behind an old cooking range. Covered in more than 100 years of dust, they were not at first recognised for their worth.

The larger of the two recovered panels depicts a group of Babylonian prisoners and has now been determined to have come from the walls of an Assyrian palace originally built by Sennacherib in 704-681 BC. This panel shows signs of having been re-carved to include scenes from around 640 to 620 BC.

"Both the wall panels found at Eastnor are unique historical pieces," says Dr Julian Reade of the British Museum, who travelled to Herefordshire to authenticate the find. "It would be quite impossible to put a price on them."

Dr Reade, a curator in the Western Asiatic Antiquities department of the BM, thinks the reliefs are typical of the kind of archaeological booty brought back in the 1930s from an area which is now part of Northern Iraq. "We have a number of similar panels here at the British Museum, but each shows a different scene. One of the Eastnor panels matches a drawing I brought with me that was made at the time of the original excavations near Mosul - in the remains of the ancient city known as Nineveh. The other panel I could not so conclusively identify," he says. He suspects it was once part of Ashurbanipal's North Palace, also near Nineveh.

The Hervey-Bathursts were thrilled by the secret of their cellar. They knew, for a start, that the panels were likely to prove an added draw for the tourists who visit Eastnor every summer. "We were all very excited," says Sarah Hervey-Bathurst. "And, as we looked at the panels, it was hard to believe quite how old they were."

The day after the discovery brought new revelations. In an ante-chamber stuffed with old documents, Imogen found a letter which put the archaeological history of the Assyrian panels in its proper context. Dated 6 April,1847, it was addressed to her ancestor Charles Somers, Viscount Eastnor, and had come from his old friend Charles Layard, the explorer and archaeologist. "I found the letter in a little room that had always fascinated me," says Imogen. "You have to climb up through a hole in the cellar to get in."

Sent from the site of the dig at Nineveh, the letter described how Layard had excavated buried Assyrian palaces and unearthed hundreds of ancient artefacts. "Imagine a labyrinth of chambers," he wrote, "leading one into another by entrances formed sometimes by gigantic human-headed lions or bulls, and others by winged mythological figures. The chambers are constructed with slabs of limestone ... "

He later made a gift of two panels to Lord Eastnor and gave others to Lady Charlotte Guest, who lived at Canford Manor in Dorset - now run as a private school. Four years ago one of the Guests' panels was memorably revealed under layers of whitewash in the school tuck shop. It eventually sold at Christies for pounds 7m.

The battle scenes shown in relief on the wall panels caused a sensation in Victorian Britain when Layard brought them home because they were thought to prove the historical authenticity of the Old Testament. Religious traditionalists felt the historical record they provided was a substantial riposte to the Darwinian arguments that were undermining the authority of the Bible.

Eastnor Castle, Ledbury (01531 633160), is open Sun-Fri to 31 Aug; and Sun only to 4 Oct.