Turner's Rome, from Mount Aventine to Sell at Sotheby's for $66.2 M.

Sotheby's will offer J.M.W. Turner's Rome, from Mount Aventine (1836) with an estimate of £50 million ($66.2 million) at its Old Master Evening Sale in London on December 9.

Before the auction, the painting will go on view at Palazzo Rondinini, an 18th-century Baroque palace in Rome, through October 1.

The work is one of the few Turners still in private hands. According to Sotheby's, Turner conceived and mapped out the painting in Italy and completed it in London. The artist painted it on commission for British art collector Hugh Andrew Johnstone Munro of Novar, a close friend who asked for a picture showing Rome bathed in a golden light.

The painting's provenance is unusually well documented. In 1876, some four decades after its completion, Archibald Primrose, 5th Earl of Rosebery and a future British prime minister, acquired it for £6,142 — roughly £636,165 in today's money — as a wedding gift for his marriage to Hannah de Rothschild, then the wealthiest woman in Britain.

The Rosebery family held the painting for more than 130 years. It has appeared at auction only once before: in 2014, the family consigned it, and it sold for £30.3 million, equivalent to about £43.47 million today. The current estimate would mark a substantial jump from that result.

The canvas carries another distinction. In its 191-year history, Rome, from Mount Aventine has never been relined or restored, and it remains on its original canvas and frame — a rarity for a painting of its age and market value.

Julian Gascoigne, senior specialist of British paintings at Sotheby's London, framed the work's significance in a statement. "Few paintings capture Turner's genius as vividly and completely as this extraordinary vision of Rome's timeless beauty," Gascoigne said. "Created at the height of his powers, it is a work of extraordinary ambition, beauty and innovation, one that has come to define not only Turner's achievement but the very course of modern painting."

If the painting reaches its estimate on December 9, it will set a new benchmark for the artist at auction and test the depth of demand for museum-grade Turners among private buyers.