In this paper we offer an institutional interpretation of the use of sortition in history. Since Ancient Greece and Italian Renaissance the use of lot has been aimed at reducing the concentration of political power and curbing factionalism. This is because factionalism was usually assumed to be detrimental to public affairs, as public officers may favour their own faction instead of pursuing the general interest. Indeed, they tend to engage in power struggles with opposing factions, unlikely to benefit society. The point is that introducing adequate portions of unpredictability in the mechanisms of political selection prevents political factions from developing and therefore avoids its detrimental effects. We present some historical cases of struggle against factionalism, which has been conducted by practising lot. Moreover, we show the recent revival of proposals of sortition as means to fight elites. Finally, we explain how sortition may be meant as an instrument able to improve -and not to substitute for- parliamentary democracy.