Introduced in 1962 and made at least through 1965. Four Square appeared in a 1964 advertisement in "House Beautiful" magazine. A 1965 Viking Glass Catalog Supplement shows 4 different Four Square items. A tall footed vase #1484, 7.5" square footed compote #1483, 8" footed large mouth vase #1485, and the 8 1/2" footed covered candy dish.
Reference: "Viking Glass 1944-1970" by Dean Six (page 90)
