Military enthusiasts dressed in Soviet Army uniforms sit on a Soviet designed T-54 tank during an exhibition at central Prague's Wenceslas Square August 21, 2008. The exhibition "Prague 1968" commemorates the 40th anniversary of the invasion by Warsaw Pact armies in then Czechoslovakia. On the night of August 20-21, 1968, more than 200,000 Warsaw pact troops including the Soviet Union, Bulgaria, East Germany, Hungary and Poland entered Czechoslovakia to halt a period of political liberalization. [Agencies]