For over 120 years the late summer music festival known as the BBC Proms has been presenting memorable concerts in London, but one of the MOST memorable occurred on today’s date in 1968.

The scheduled performers at the Royal Albert Hall were the USSR State Symphony, its conductor Yevgeny Svetlanov, and the virtuoso cellist Mstislav Rostropovich. As the musicians took to the stage, boos and cat-calls were mixed with the applause, and some shouts of “Go home!” and “Russians out!”

The reason? Earlier that same day, the Soviet Union and its East Block allies had invaded Czechoslovakia, sending troops and tanks into the country to crush the so-called “Prague Spring,” a period of liberalization and reform that threatened Communist control of that nation.

By a cruel stroke of irony, one of the works on the scheduled program of the Soviet orchestra was the Cello Concerto of Czech composer Antonin Dvorak. There were some shouts of protests as Rostropovich began to play, but by the end of his intense performance, all was quiet. Rostropovich had played with tears streaming down his face, and after finishing held up the conductor’s score of the concerto as both a sign of solidary with the Czech nation and act of mute protest of the invasion.