1937 (01.20), 17th Extraordinary (the last) All-Russian Congress of Soviets, which took place in January 15-21 and approved the new edition of the Constitution of 1937, cover from the Congress sent in Moscow, franked by two air post values, tied by special Congress violet date stamp and text ''S'ezdovskaya'', postmarked on arrival, mainly VF and rare item of Soviet History, about 1400 delegates were participated in the Congress and more than two thirds were repressed and even shot during the Great Purge, Est. $200-$250 (Image)