SHE lies naked on a silk grey sheet, her beautiful bum, her slender waist, her blemish-free white skin catching the eye. She is Venus, the Roman goddess of love, the personification of beauty, the lady of Teesdale.

She's propped up on her elbow, fixated by her reflection in the mirror, transfixed by her beauty. Cupid, holding the mirror, is similarly entranced.

But the reflection in the mirror is indistinct. The beauty, despite the delicious curves of the bum, could be faded, its youth could be aged.

Or does the Rokeby Venus know we are there? When she lifts her eyes from her beauty, will she - in her naked vulnerability - in the mirror see us, standing there, ogling her bum? Does she care?

Arty London has this week been agog at the vixen Venus. She is the star of an exhibition of paintings by the greatest Spanish painter, Diego Rodriguez Velazquez de Silva, at the National Gallery - the exhibition opened on Monday with a record 13,000 tickets sold in advance.

The painting is known variously as Venus at her Mirror, The Toilet of Venus or Venus and Cupid; it is known commonly as the Rokeby Venus because for 100 years it hung in Teesdale near where the Greta meets the Tees.

Venus was painted around 1650. Who she was, no one knows - possibly Damiana, a scandalous actress; probably no one, just a figment of Velazquez' fertile imagination. She is, though, unique: the Catholic church disapproved of such immodest display. Anyone exhibiting her would have expected the Spanish Inquisition.

She remained for the private enjoyment of leading Spanish ministers until she was smuggled out to escape the Napoleonic War. In 1813 she was acquired by John Bacon Sawrey Morritt, the MP for Northallerton.

He lived in Rokeby, a Palladian hall built in 1735 by the eccentric amateur architect Sir Thomas Robinson. Sir Thomas was a top fellow: he designed the headily high Abbey Bridge over the Tees at Egglestone and the daring single span that crosses the river at Winston. His is the Gothic gateway that leads into the Bishop's park at Bishop Auckland.

Not only did Sir Thomas enjoy extravagant buildings but also extravagant parties, and his extravagant debts caused him to sell the hall to the Morritts in 1769. They own it to this day, a spot - despite the ugly, noisy scar of the nearby A66 - as delightful as Venus' bum, which has inspired poet Sir Walter Scott and painter JMW Turner.

In 1905, the Morritts needed to liquidate their Venus. These were patriotic days. Britain was trying to out-do Germany in everything from colonies to warships to armaments to art works. Berlin coveted the Rokeby Venus; London had to be victorious, and so the Teesdale temptress became the first work of art to be acquired by the British nation at a cost of £45,000.

She hung in the National Gallery until March 10, 1914, when militant suffragette Mary "Slasher" Richardson attacked her with a chopper, inflicting seven ugly wounds on that sensuous white back.

"Slasher" was enraged by the recent arrest of Emmeline Pankhurst. "I have tried to destroy the picture of the most beautiful woman in mythological history," she said, "as a protest against the Government for destroying Mrs Pankhurst, the most beautiful character in modern history." Later she said she hated the way men gawped at Venus.

This week Londoners have been gawping at the Rokeby Venus in their thousands - and while interpreting her enigma have been mispronouncing her name. The original de Rokeby family probably came over with William the Conqueror in 1066 and called themselves "Rookby", which is still the way they say it in this corner of Teesdale.