The St. Louis Monument is a monument located in St. Louis, Missouri. It is a memorial to the city's French colonial past and was designed by architect Eero Saarinen. The monument is an ARCH made of stainless steel and is 630 feet tall. It is the tallest ARCH in the world and is a popular tourist attraction. The four-letter solution to the crossword is ARCH, which is the same as the type of monument it is.