Pablo Picasso may be the artist most famously associated with the Spanish civil war, but as the rifles fired in revolutionary Catalonia, it was those on the frontlines who first captured the conflict. One of the most important was José Luis Rey Vila, whose sketches brought the rhythms of war to life in bold, blocky lines with splashes of intense colour.Full of urgency and movement, many of his sketches document anarchist militias engaged in street battles; others depict more sanguine scenes after the fighting stopped. In charcoal and watercolours, Rey Vila produced arresting portraits of red-capped volunteers, nurses tending the...