Dozens of rare prints and drawings by Dutch artist M.C. Escher have been sold at an online auction in New York for more $7.8 million, or around €6.7 million—far exceeding expectations.

Auction house Christie’s sold 65 pieces by the graphic artist, who was born in Leeuwarden in 1898 and died in 1972. Many of the works had rarely, if ever, appeared on the market before, and several included preparatory sketches for some of Escher’s best-known pieces. On average, the lots sold for around four times their estimated value.

Among the highlights was Day and Night, which had a top estimate of €30,000 but sold for around €140,000, local broadcaster Omrop Fryslân reported. A pencil sketch for Relativity—featuring Escher’s famous never-ending staircases—fetched nearly half a million euros, ten times the original estimate.

Escher is best known for his visual illusions and mind-bending use of architecture and perspective. Over the course of his career, he produced 448 lithographs, woodcuts and wood engravings, as well as more than 2,000 drawings and sketches. He also illustrated books and designed carpets and banknotes.

The works came from the private collection of 88-year-old American filmmaker Robert Owen Lehman Jr., who acquired them over the past 50 years. “I look forward to seeing these great works pass on to new collectors, because owning them has been a labour of love,” he told Christie’s.

Proceeds from the sale will go to a foundation Lehman set up to promote appreciation of classical music. “And since Escher was as passionate about music as I am,” he said, “I trust he would have approved.”