San Diego

That first fence was a line of surplus helicopter landing pads, welded together. It stopped vehicles but not climbers, so a taller secondary layer came in 1996. Then came a third layer, including at Friendship Park, the one place where families not permitted to travel between the countries can gather to talk through mesh.

Nearly six miles east of Friendship Park is the port of entry at San Ysidro, which is the most heavily traveled in the Western Hemisphere; 135,000 people cross there each day.

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