Imagine a breaking story on the evening news. A camera in a helicopter pans the waterfront of a major port city, where two angry mobs face off on the deck of a pier. A much larger crowd behind a fence shouts encouragement or threats. This is the setting of Strike on the Pier (cover), by the Mexican painter David Alfaro Siqueiros (1896-1974). Although the protesters cannot be seen clearly, they appear to be raising their arms and shouting. Magnification is not helpful, because the mobs are sketched as collective units rather than as individuals with distinguishing features. Wind-whipped waves and passing cloud shadows increase the tension of the scene. In his landscapes, such as Twilight (JAMA cover, October 17, 2012), Siqueiros has a way of summoning the forces of nature to create a mood. Strike on the Pier does not engage the viewer directly, because the subjects are so far away, but it is clear that a human struggle is taking place, probably over working conditions—and for Siqueiros, a lifelong workers' activist, the specific issues were less important than seeing workers stand up for their rights. This landscape demonstrates how the structure of an urban environment can promote social dissent by providing large public spaces where people from all walks of life are free to gather and express their opinions.