The Schiphol air traffic control tower, with a height of 101 m (331 ft), was the tallest in the world when constructed in 1991.[citation needed] Schiphol is geographically one of the world's lowest major commercial airports. The entire airport is below sea level; the lowest point sits at 11 ft (3.4 m) below sea level (or 4.5 ft (1.4 m) below the Dutch Normaal Amsterdams Peil (NAP)); the runways are around 3 m (9.8 ft) below NAP.