Until the early 20th century, construction was largely limited to the slightly higher ground along old natural river levees and bayous; the largest section of this being near the Mississippi River front. This gave the 19th-century city the shape of a crescent along a bend of the Mississippi, the origin of the nickname "The Crescent City." Between the developed higher ground near the Mississippi and the shores of Lake Pontchartrain, most of the area was wetlands only slightly above the level of Lake Pontchartrain and sea level. This area was commonly referred to as the "back swamp," or areas of cypress groves as "the back woods." While there had been some use of this land for cow pasture and agriculture, the land was subject to frequent flooding, making what would otherwise be valuable land on the edge of a growing city unsuitable for development. The levees protecting the city from high water events on the Mississippi and Lake compounded this problem, as they also kept rainwater in, which tended to concentrate in the lower areas. 19th century steam pumps were set up on canals to push the water out, but these early efforts proved inadequate to the task.