Through a critical discussion of the role and functioning of sketching in architectural design, followed by the analysis of a set of travel sketches by Le Corbusier, this study has investigated the process of architectural travel sketching, finding that besides recording site specific information, travel drawing requires similar pictorial reasoning and conceptual decision making to that involved in design sketching. Travel drawing matters because the process of sketching in situ makes one observe, understand, learn and remember the essential architectural ideas of the subject matter. The architect's informed personal interpretation combines the artistic conscience with the information observed and with prior knowledge of the subject, creating an individual record of thoughts and impressions made in situ, which may be recalled and reused later on. Travel drawing can also form the first step in the design process by suggesting starting points for subsequent designs rooted in the architect s holistic perception of the specific character and attributes of a place. This study concludes that travel drawing and design sketching are profoundly linked, and that the significance of travel drawing lies partly in its ability to influence and enrich the creative process of architectural design.Illustrated with diagrams and travel sketches by the author and major 20th century architects. The practical part consists of the graphic analysis of a set of Le Corbusier's sketches of the Acropolis, from his Voyage to the Orient, Carnet 3, 1911. These sketches have been grouped into 3 sets to show the development of Le Corbusier's major architectural ideas about the Acropolis. Each drawing is analysed with the author''s diagrams to illustrate tone, outline and composition - categories which have been chosen for being the most significant aspects of Le Corbusier's pencil sketches. These diagrams highlight which aspects of the architecture have been emphasised in each sketch. Through comparing these diagrams, the overall development of Le Corbusier's architectural understanding of the Acropolis may be followed. Inconsistencies or anomalies are then examined with further diagrams showing alternative compostions or tones, in order to suggest why one method has been chosen over the others. This analysis proposes a new explanation and title for one of the original sketches. The conclusions have been illustrated with a set of the author s recent drawings, studying two buildings by the Modernista architect Josep-Maria Jujol.