Why did the east built the Berlin wall?

Anyone who had skills that could be sold in the West, like doctors and engineers, were defecting from East Germany to West Germany. (Oh yeah...they forgot to tell you. The East Germans built another "wall" - well, fence - along the border between East and West Germany.) The Soviets told East German dictator Walter Ulbricht to think of a way to stop the defections from happening, and Ulbricht decided to build a wall all the way around West Berlin.