Raphael’s portrait of Florentine ruler Lorenzo de’ Medici, almost five centuries old, has been priced by Christie’s International at little more than a 1962 Andy Warhol image of Marilyn Monroe.

Christie’s top estimate for the Raphael at a July 5 sale in London is 15 million pounds ($29.6 million). Warhol’s “Lemon Marilyn,” showing a purple-faced Monroe on a yellow background, sold for $28 million in New York last week, including commission.

The Raphael valuation shows how art that has survived for hundreds of years is losing ground as new millionaires opt for contemporary pictures.

Works by Raffaello Sanzio, known as Raphael, are mostly in museums, so there are few opportunities to buy them. The portrait of Medici, ruler of Florence in the early 16th century, is being sold by collector Ira Spanierman. Mr. Spanierman bought it at a New York auction in 1968, Christie’s said in a statement released yesterday.

Raphael, who died in 1520, was commissioned by Pope Julius II to paint frescoes in a papal room in the Vatican. He also worked for the next pope, Leo X, who was the uncle of Lorenzo de’ Medici, Christie’s said.

Scholars in the late 19th century weren’t convinced that Raphael was the painter of the portrait or Medici was the subject, wearing a fur-trimmed cape and tunic, Christie’s said.

“All major scholars of the artist” now accept the current attributions, influenced by an article published in 1971 by Konrad Oberhuber, the company said.

Christie’s and Sotheby’s hold sales of old master pictures in the British capital in July. The biggest such auctions in recent years were in 2005, when they fetched more than 100 million pounds, after a Canaletto painting of Venice set a record of 18.6 million pounds on a day of terrorist bombings.