RESEARCH IMW tape 205 cuba 1961 and berlin wall is built

The US launched airstrikes to disable Castro's Air Force during an invasion, but President Kennedy limited them. Castro's forces quickly overran the invaders, who were later ransomed back to the US. Following this, the Soviet Union strengthened its control over Eastern Europe, symbolized by the construction of the Berlin Wall in 1961, which sealed off East Germany from the West.

What significant construction symbolized the Soviet grip on Eastern Europe?

What was the purpose of the Berlin Wall according to the text?