Measured by the number of apprehensions or arrests at the border, it was quickly apparent that building fences and massing Border Patrol agents was a powerful deterrent to illegal crossing in the places where it was deployed. In the El Paso sector, the decline in apprehensions was almost immediate following Operation Hold the Line, falling from 250,000 in 1992 to fewer than 80,000 by 1994. In the San Diego sector, apprehensions fell more gradually but still dramatically, from more than 550,000 in 1992 to just 110,000 in 2001 (CBP 2016a). But it was also equally apparent that sealing the high-traffic corridors alone would not significantly reduce illegal crossings. Instead, border crossers move to the more remote regions in Arizona, and the numbers continued to climb