Small selection form "Crossings" exhibition.
Many North Americans perceive the U.S.-Mexico border as a fence or a wall, some sort of barrier erected to keep out the peoples to the south. And since 1995, when a more protectionist U.S. immigration policy was enacted, and further intensified in 2001 by fears of terrorism in a post 9-11 world, the border has seemed more like a barrier than perhaps ever before.

However, if one takes the long view, one realizes that the nature of the border - especially the degree of its porousness - has always reflected changes in U.S. attitudes toward Mexico and...