This is a small version of the map and you can see how it was surrounding a lot of the city, and that is 26 miles! That was how they captured so many people, because they were leaving so fast.
As you can see here, they put barbed wire on the already 9 foot tall wall, to make sure nobody got over.
(Croan, Melvin. "Berlin Wall." World Book Advanced, World Book, 2019 www.worldbookonline.com/advanced/article?id=ar056660. Accessed 11 Jan. 2019)
If you want to know all of the facts, click here to see article.