The border between the United States and Mexico stretches 3,169 kilometers (1,969 miles), crossing deserts, rivers, towns, and cities from the Pacific to the Gulf of Mexico. Every year, an estimated 350 million people legally cross the border, with another 500,000 entering into the United States illegally. No single barrier stretches across the entire border, instead, it is lined with a patchwork of steel and concrete fences, infrared cameras, sensors, drones, and nearly 20,000 U.S. Border Patrol agents. As immigrants from Mexico and other Central and South American countries continue to try to find their way into the U.S., Congress is now considering an immigration reform bill called the Border Security, Economic Opportunity and Immigration Modernization Act of 2013. The bill proposes solutions to current border enforcement problems and paths to citizenship for the estimated 11 million existing illegal immigrants in the U.S. Gathered here are images of the US-Mexico border from the past few years.