On the night between the 12th and the 13th of August 1961, the police and units of the East German army began to close the border and, by Sunday morning, the border with West Berlin was closed. East German troops and workers had begun to tear up streets running alongside the border to make them impassable to most vehicles and to install barbed wire entanglements and fences along the 156 kilometers (97 miles) around the three western sectors, and the 43 kilometers (27 miles) that divided West and East Berlin. The barrier was built inside East Berlin or East German territory to ensure that it did not encroach on West Berlin at any point. Generally, the Wall was only slightly inside East Berlin, but in a few places it was some distance from the legal border. Later, the initial barrier was built up into the Wall proper, the first concrete elements and large blocks being put in place on 17 August.
Finally, if you travel Europe and you see two German groups at a campground, you might easily be able to distinguish them. Eastern Germans usually sleep in tents, while western Germans prefer to travel with trailers. We did not find a scientific explanation, but one might posit that it's rooted in western Germans' longer experience traveling the world. Furthermore, many young eastern Germans couldn't even afford a car under communism. Trying to buy a trailer would have been more expensive and nearly impossible for most eastern Germans. While those in the west were able to explore beyond their borders, eastern Germans remained practically imprisoned by their government for nearly 30 years -- until 25 years ago.