On 15 and 16 September, Sotheby's auctioned 287 works by Damien Hirst, and once again the number of zeros has been the main talking point, together with much debate about the craziness of the prices paid for contemporary art. (Hirst's jewel-encrusted skull, whose alleged asking price is £50m, does also make the Titians look positively reasonable.) As it happens, however, one of the most striking things about the visual arts canon is its changelessness. It is true that there have inevitably been ups and downs, perhaps the most notable being the fall from grace and only relatively recent rise again of Caravaggio, just as there have been real rediscoveries - Vermeer and Georges de la Tour being the most arresting among major figures. But by and large the old masters who are most revered today were always at or near the top of the tree. The misunderstood genius working in a garret and unappreciated by his contemporaries - step forward Vincent van Gogh - is a purely 19^th- and 20^th-century phenomenon.

All of this strongly suggests that today's collectors, especially if they are willing to be patient and not cash in their artworks too soon, could do a lot worse than invest in Damien Hirst. Hirst himself, meanwhile, is reported to have become part of the illustrious tradition of artists who collect art (in his case, inter alia, Francis Bacon). Intriguingly, one of Titian's late masterworks - the sulphurous Crowning with Thorns in Munich - was owned by Titian's younger contemporary and would-be rival, Tintoretto.

Nearer to home, by 1641 the Titian group portrait of the Vendramin Family, now safely in Trafalgar Square, belonged to another imported element of our national heritage, Sir Anthony van Dyck. A few years later, around 1644, it passed into the possession of the wonderfully named Sir John Wittewronge as part repayment of a debt owed by Sir Richard Price, who had married Van Dyck's widow. Wittewronge sold it the next year to the 10^th Earl of Northumberland, and his descendant, the seventh Duke of Northumberland, sold it to the National Gallery in 1929. Naturally there was much wailing and gnashing of teeth at the price, which seemed so immense at the time, but perhaps less chippy anti-ducal sentiment. It cost the then princely - or should that be ducal? - sum of £122,000.