See M. Gelzer, The Roman Nobility (1969); R. J. A. Talbert, The Senate of Imperial Rome (1984).
Modern democratic states with bicameral parliamentary systems are sometimes equipped with a senate, often distinguished from an ordinary parallel lower house, known variously as the "House of Representatives", "House of Commons", "Chamber of Deputies", "National Assembly", "Legislative Assembly", or "House of Assembly", by electoral rules. This may include minimum age required for voters and candidates, proportional or majoritarian or plurality system, and an electoral basis or collegium. Typically, the senate is referred to as the upper house and has a smaller membership than the lower house. In some federal states senates also exist at the subnational level. In the United States all states other than Nebraska have a state senate. In Australia all states other than Queensland have an upper house known as a legislative council. Several Canadian provinces also once had legislative councils, but these have all been abolished, the last being Quebec's Legislative Council in 1968.
Senate membership can be determined either through elections or appointments. For example, elections are held every three years for half the membership of the Australian Senate, the term of a senator being six years. In contrast, members of the Canadian Senate are appointed by the Governor General upon the recommendation of the Prime Minister of Canada, holding the office until they resign, are removed, or retire at the mandatory age of 75. Some states have a combination of these two approaches, such as the Jamaican Senate, where thirteen are appointed by the prime minister and eight by the leader of the opposition. In larger countries, the senate often serves a balancing effect by giving a larger share of power to regions or groups which would otherwise be overwhelmed under strictly popular apportionment.