Circa 1504, Raphael executed a pen and ink sketch, today in the Louvre Museum, in which the subject is flanked by large columns. Experts universally agree it is based on Leonardo's portrait of Mona Lisa. Other later copies of the Mona Lisa, such as those in the National Museum of Art, Architecture and Design in Oslo and The Walters Art Museum in Baltimore, also display large flanking columns. As a result, it was originally thought that the Mona Lisa in the Louvre had side columns and had been cut. However, as early as 1993, Zöllner observed that the painting surface had never been trimmed. This was confirmed through a series of tests conducted in 2004. In view of this, Vincent Delieuvin, curator of 16th-century Italian painting at the Louvre museum states that the sketch and these other copies must have been inspired by another version, while Frank Zöllner states that the sketch brings up the possibility that Leonardo executed another work on the subject of Mona Lisa.