The original impetus to build Prospect Park stemmed from an April 18, 1859, act of the New York State Legislature, empowering a twelve-member commission to recommend sites for parks in the City of Brooklyn. At the time, Brooklyn was the world's first commuter suburb, and it eventually became the third largest city in the country after New York and Philadelphia. During this time, concepts concerning public parks gained popularity. In 1858, Frederick Law Olmsted and Calvert Vaux had created Central Park in Manhattan, which became the first landscaped park in the United States. James S. T. Stranahan, then President of the Brooklyn Board of Park Commissioners, believed that a park in Brooklyn "would become a favorite resort for all classes of our community, enabling thousands to enjoy pure air, with healthful exercise, at all seasons of the year..." He also thought a public park would attract wealthy residents. In February 1860. a group of fifteen commissioners submitted suggestions for locations of four large parks and three small parks in Brooklyn, as well as a series of boulevards to connect said parks. The largest of these proposed parks was a 320-acre (1.3 km2) plot centered on Mount Prospect and bounded by Warren Street to the north; Vanderbilt, Ninth, and Tenth Avenues to the west; Third and Ninth Streets to the south; and Washington Avenue to the east. Egbert Viele began drawing plans for "Mount Prospect Park", as the space was initially called, and published his proposal in 1861. The park was to straddle Flatbush Avenue and include Prospect Hill, as well as the land now occupied by the Brooklyn Public Library, Brooklyn Botanic Garden, and Brooklyn Museum. By late 1860, land had been purchased for Viele's plan. However, the onset of the Civil War stopped further activity, and the boulevards and smaller parks were pushed back. The delay prompted some reflection; Stranahan invited Calvert Vaux to review Viele's plans early in 1865. Vaux took issue with Flatbush Avenue's division of the park, thought that the park should have a lake, and urged for southward expansion beyond the city limits and into the then-independent town of Flatbush.:86–91 Vaux's February 1865 proposal reflected the present layout of the park: three distinctive regions, meadow in the north and west, a wooded ravine in the east, and a lake in the south, without being divided by Flatbush Avenue. Vaux included an oval plaza at the northern end of the park, which would later become Grand Army Plaza. The revised plan called for purchase of additional parcels to the south and west to accommodate Prospect Lake, but it excluded parcels already purchased east of Flatbush Avenue, including Prospect Hill itself. In addition, engineer-in-charge Joseph P. Davis and assistants John Bogart and John Y. Culyer were named to work on the project.