The town of Nogales is split down the middle by the US/Mexico border. In these pictures Mexico is on the left, and the US is on the right. In 1898 you could cross anywhere. Now there is a 15 foot high wall and border patrol agents every 50 yards.
You can still see many of the same buildings on the Mexican side, but only a few remain on the American side. Here is each side of the border for comparison:
Somebody should take this picture again in 2108.
This is a closeup of the wall taken from the US side. Cutting torch appears to be a popular way to immigrate to the US. There are patches like these all over the wall.
The 1898 photo is from US National Archives | Photos of the American West: 1861-1912 (#163).