Constantijn Huygens II was a Dutch diplomat, poet, collector of prints and drawings, and amateur draughtsman of landscapes with an interest in the sciences. His father, the statesman Constantijn Huygens I (1596-1687), acquired a camera obscura from the London-based Dutch glassmaker, engraver and engineer Cornelis Drebbel (1572-1633) in 1622 and wrote extensively on the mathematics of optics and on optical devices. Most of Huygens’s drawings were made in the course of his travels and during military campaigns. This view of the river Ijssel dated 5 June 1672 shows his characteristic lightness of touch and spontaneity in the use of layers of wash. The year before, Huygens’s brother, the mathematician Christiaan Huygens (1629-1695), had been commissioned by the States of Holland to inspect the Ijssel and the Nederrijn and to write a report on how to prevent them from silting up.