THE ROLE OF DRAWING in Monet's art changed yet again in his later career. The series pictures—such as his paintings of grainstacks, poplars, and the façade of Rouen Cathedral—were partly conceived in sketchbooks, but he did not repeat the use of such drawings for two decades. On a visit to London in 1901, he produced his last and most sustained group of pastels, all based on the Thames bridges at Charing Cross and Waterloo. Increasingly, line and color merged in Monet's works on canvas, most thrillingly in the paintings made at Giverny. Even at their grandest and most vaporous, some of the large water-lily pictures appear to have begun life as simple pencil or crayon studies, their subtle rhythms captured in a few lines that are carried through into many of his painted "studies" for the Grandes Décorations that were eventually unveiled in the Orangerie in 1927.