Until 1966, Dutch politics were characterised by pillarisation: society was separated in several segments (pillars) which lived separate from each other and there was only contact at the top levels, in government. These pillars had their own organisations, most importantly the political parties. There were four pillars, which provided the five most important parties, the socialist Labour Party (Partij van de Arbeid; PvdA), the conservative liberal People's Party for Freedom and Democracy (Volkspartij voor Vrijheid en Democratie; VVD), the Catholic Catholic People's Party (Katholieke Volkspartij; KVP) and the two conservative Protestant parties, the Christian Historical Union (Christelijk-Historische Unie; CHU) and the Anti-Revolutionary Party (Anti-Revolutionaire Party; ARP). Since no party ever gained an absolute majority, these political parties had to work together in coalition governments. These alternated between a centre-left "Roman/Red" coalition of PvdA, KVP, ARP and CHU and a centre-right coalition of VVD, KVP, ARP and CHU.