Over the centuries, it has been common to reuse canvases and paint over murals, meaning that many great works of art have been lost between layers of paint. Fortunately, modern technology and notes on the originals lets us see those hidden masterpieces once again.

The Battle of Anghiari, by Leonardo Da Vinci (1452-1519), painted in 1505, now behind a section of a fresco by Giorgio Vasari (1511-1574) in the Hall of the Five Hundred (Salone dei Cinquecento), Palazzo Vecchio, Florence, Italy

A copy of its central section is known, thanks to a drawing by Peter Paul Rubens, 1603, which was based on an engraving of 1553 by Lorenzo Zacchia:

The project was abandoned by Leonardo because its upper part couldn't dry fast enough and the colors intermingled.

(via Wikimedia Commons)

The Portrait of Isabella Romola de' Medici, under the 19th century portrait of Eleanor of Toledo. The original was painted around 1570-1574, and attributed to Allesandro Allori


(via Carnegie Museum of Art)

A beached whale on View of Scheveningen Sands, created by Hendrick van Anthonissen (1605-1656), around 1641, had been hidden for more than 150 years


(via The History Blog)

A bust of Napoleon's son in the upper left corner of Portrait of Jacques Marquet de Montbreton de Norvins by Jean Auguste Dominique Ingres (1780-1867), 1812


(via Wikiart)

Portrait of Napoleon Bonaparte's brother Joseph, who was the King of Spain between 1808 and 1813 as José I, under the Portrait of Don Ramón Satué, a Spanish judge, by Francisco José de Goya y Lucientes (1746-1828), 1823


(via WikiArt and ABC)

Two half-naked wrestlers, one of Vincent Van Gogh's (1853-1890) homework as an art student, behind Still Life with Meadow Flowers and Roses, 1886


(Photo by AP/Kroeller Mueller Museum and WikiArt)

The portrait of a woman behind Patch of Grass, by Vincent Van Gogh (1853-1890), 1887


(via Google Art Project/Wikimedia Commons and DESY)

A portrait of a bearded man underneath The Blue Room, by Pablo Picasso (1881-1973), 1901


(Photos by The Phillips Collection/AP)

A woman with a child, a bull and a sheep, behind The Old Guitarist, by Pablo Picasso (1881-1973), 1903-1904


The hidden painting with a detail from a letter wrote by Picasso himself:


(via WikiArt, Medill Reports, Wikimedia Commons and The Art Institute of Chicago)

A portrait of a man beneath Woman Ironing, by Pablo Picasso (1881-1973), 1904


(via Guggenheim)

An illustration of a fist fight, appeared in a 1919 article in Everybody's Magazine, behind Family Portrait, an oil painting by Newell Convers Wyeth (1882-1945), 1924


(via WHYY and Winterthur)