The original World Trade Center complex in Lower Manhattan, New York City consisted of seven buildings including two landmark twin towers that were destroyed in the September 11, 2001 attacks. The towers were designed in the early 1960s and constructed between 1966-1973, becoming the tallest buildings in the world at the time. On September 11, 2001, terrorists hijacked two planes and crashed them into the North and South towers, causing both to collapse and killing over 2,600 people. A memorial now stands at the site, known as Ground Zero.