In the Cyprus crisis of 1963–64, in the aftermath of unilateral constitutional changes by the Greek Cypriots, intercommunal violence broke out. Nicosia was divided into Greek and Turkish Cypriot quarters by the Green Line, named after the colour of the pen used by the United Nations officer to draw the line on a map of the city. This resulted in the ceasing of Turkish Cypriot participation in the government, and following more intercommunal violence in 1964, a number of Turkish Cypriots moved to the Turkish quarter of Nicosia, causing serious overcrowding.