 The culmination of St. Louis modern architecture is Eero Saarinen's magnificent stainless-steel gesture, the Gateway Arch, centerpiece of the riverside Jefferson National Expansion Memorial.The earliest buildings in St. Louis were constructed in the French Colonial style.Although Spain took possession of the Louisiana territory in 1764 via the Treaty of Fontainebleau (1762) and the Treaty of Paris (1763) (and defended against a French rebellion in 1768), St. Louis remained largely a refuge for French settlers.