Unlike the Bois de Boulogne and Bois de Vincennes, the site for the future park did not have any trees or other vegetation. It was largely occupied by a large stone quarry, and to make the work more complicated, it was above a network of tunnels of abandoned mines, which were filled with human skeletons. These tunnels were part of the ossuary of Paris, popularly known as the catacombs of Paris, where the remains of some six million Parisians had been moved at the end of the 18th century. Before construction of the park could begin, some eight hundred skeletons were removed from the tunnels. The work was also complicated by the track of the railroad line which circled Paris, which passed directly through the site.