Politics, need, cost, location, and geography of the site, as well as technology available at the time of construction influenced lighthouse designs. Before the mid-19th century, lighthouse construction technology required solid rock or other stable foundation soils; onshore towers sometimes proved inadequate to warn ships off a shoal located offshore. In some locations a lighted buoy or a lightship solved this problem. Riverine and estuarine environments, however, often had unstable muddy and/or sandy bottoms which could not support the heavy masonry towers then in vogue. In areas such as the Chesapeake Bay, Delaware Bay, the Gulf of Mexico, the Mississippi River delta, and the coral reefs of the Florida Keys, the development of newer technology using screwpile, caisson, and skeletal tower lighthouse construction was essential to adequately lighting the marine hazards.