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. 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 the 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.