In many cases it is possible to identify the sources from which Jan de Bisschop copied his Italianate landscapes and town views. A Map of Rome, drawn by Jan de Bisschop and engraved by J. Lamsvelt (fig. i), is likewise based on an earlier example, Matteo Gregorio De Rossi's map of I668. One of the items in the exhibition devoted to Jan de Bisschop at the Rembrandthuis, Amsterdam, from December I9 I992 to February 28 I993, was a Panorama of Rome from the Pierpont Morgan Library in New York (fig. 3). The author, Michiel Plomp, asserts that Jan de Bisschop based this work on the Panorama of Rome by Theodoor Matham, who was active in Rome between I633 and I637. Hitherto only two sections of Matham's panorama were known in the Print Room of the Rijksmuseum in Amsterdam (figs.4a and b). For a proper comparison of the two panoramas, Matham's third, right-hand section showing a View of Castel S. Angelo and S. Pietro, should be taken into consideration (figs.2 and 4c). This drawing is kept in the Kennemerland Archive Office at Haarlem. Matham's panorama can be dated to I637-I645, after his return to Amsterdam. In the catalogue of the sale of the Neyman collection planned for late June I776 in Paris, the three sections of Matham's panorama are still listed as a single lot. Compositionally, the two panoramas are very similar. Both extend from the Villa Medici to S. Pietro, and both are seen from two different viewpoints north of the Porta del Popolo. However, a few differences can also be observed. Some of the topographical elements are more distinct in Jan de Bisschop's panorama than in Matham's: the shape of Bernini's belfry, the position of the Obelisco Flaminio on the Piazza del Popolo, and the course of the Tiber. It is therefore highly unlikely that Jan de Bisschop based his panorama on the sections of Theodoor Matham's in Amsterdam and Haarlem. Did Jan de Bisschop perhaps consult Matham's preliminary, on-the-spot sketches? Or are we to assume that a third draughtsman is involved, and that both Matham and De Bisschop based their panoramas on his work?