In Baltimore's early years, the Gwynns Falls lay beyond the city's settled area. During the 19th century, rapid population growth pushed the boundaries westward by annexing new areas in the valley and then beyond. Through the years of expansion, the rowhouse was the preferred residential type, providing economies of scale and affordable housing for working-class residents. Street-front white marble steps, scrubbed frequently, became a well-known Baltimore trademark. Rowhouses distinguished themselves from one neighborhood to another with modest decorative and design features in keeping with the architectural styles of the time. After World War II, they lost popularity to suburban detached homes. In recent years, rowhouses along the Gwynns Falls Trail have enjoyed a revival.