The ancient writers saw very clearly that each principle of government standing alone is carried to excess and provokes a reaction. Monarchy hardens into despotism. Aristocracy contracts into oligarchy. Democracy expands into the supremacy of numbers. They therefore imagined that to restrain each element by combining it with the others would avert the natural process of self-destruction, and endow the State with perpetual youth. But this harmony of monarchy, aristocracy, and democracy blended together, which was the ideal of many writers, and which they supposed to be exhibited by Sparta, by Carthage, and by Rome, was a chimera of philosophers never realised by antiquity. At last Tacitus, wiser than the rest, confessed that the mixed Constitution, however admirable in theory, was difficult to establish and impossible to maintain. His disheartening avowal is not disowned by later experience. The experiment has been tried more often than I can tell, with a combination of resources that were unknown to the ancients--with Christianity, parliamentary government, and a free press. Yet there is no example of such a balanced Constitution having lasted a century. If it has succeeded anywhere it has been in our favoured country and in our time; and we know not yet how long the wisdom of the nation will preserve the equipoise. The Federal check was as familiar to the ancients as the Constitutional. For the type of all their Republics was the government of a city by its own inhabitants meeting in the public place. An administration embracing many cities was known to them only in the form of the oppression which Sparta exercised over the Messenians, Athens over her Confederates, and Rome over Italy. The resources which, in modern times, enabled a great people to govern itself through a single centre did not exist. Equality could be preserved only by Federalism; and it occurs more often amongst them than in the modern world. If the distribution of power among the several parts of the State is the most efficient restraint on monarchy, the distribution of power among several States is the best check on democracy. By multiplying centres of government and discussion it promotes the diffusion of political knowledge and the maintenance of healthy and independent opinion. It is the protectorate of minorities, and the consecration of self-government. But although it must be enumerated among the better achievements of practical genius in antiquity, it arose from necessity, and its properties were imperfectly investigated in theory.