About a half a mile south of the Gateway Arch in downtown St. Louis, lies a two-mile long flood-wall, covered in the combined efforts of more than 250 of graffiti artists. Construction of the wall began in 1956 and took until 1964. During the Great Flood of 1993, the river reached to two feet below the top of the flood-wall, but the wall in its entirety held up to the raging Mississippi. After the flood, the large concrete wall became a spot for local graffiti artists to leave their marks….