Each of the two suspension towers, located offshore, contains around 1 million bolts and 3 million rivets. The towers contain a combined of metal, more than three times the of metal used in the Empire State Building. Because of the height of the towers () and their distance from each other (), the curvature of the Earth's surface had to be taken into account when designing the bridge. The towers are not parallel to each other, but are farther apart at their tops than at their bases. When built, the bridge's suspension towers were the tallest structures in New York City outside of Manhattan. The diameters of each of the four main suspension cables is . Each main cable is composed of 26,108 wires amounting to a total of in length. The upper and lower levels are supported by trusses underneath each roadway, which stiffen the bridge against vertical, torsional, and lateral pressure. The anchorage on the Staten Island side contains a facility for heating cinders that are used to de-ice the bridge deck during winter.