“How striking and grand is the spectacle presented by the period with which I purpose to deal, will be most clearly apparent if we set beside and compare with the Roman dominion the most famous empires of the past, those which have formed the chief theme of historians. Those worthy of being thus set beside it and compared are these. The Persians for a certain period possessed a great rule and dominion, but so often as they ventured to overstep the boundaries of Asia they imperilled not only the security of this empire, but their own existence. The Lacedaemonians, after having for many years disputed the hegemony of Greece, at length attained it but to hold it uncontested for scarce twelve years. The Macedonian rule in Europe extended but from the Adriatic region to the Danube, which would appear a quite insignificant portion of the continent. Subsequently, by overthrowing the Persian empire they became supreme in Asia also. But though their empire was now regarded as the greatest geographically and politically that had ever existed, they left the larger part of the inhabited world as yet outside it. For they never even made a single attempt to dispute possession of Sicily, Sardinia, or Libya, and the most warlike nations of Western Europe were, to speak the simple truth, unknown to them. But the Romans have subjected to their rule not portions, but nearly the whole of the world and possess an empire which is not only immeasurably greater than any which preceded it, but need not fear rivalry in the future. In the course of this work it will become more clearly intelligible by what steps this power was acquired, and it will also be seen how many and how great advantages accrue to the student from the systematic treatment of history.”

Madison's own notes on Madison's remarks of debate (6 June 1787) http://avalon.law.yale.edu/18th_century/debates_606.asp
1780s, The Debates in the Federal Convention (1787)
Context: In all cases where a majority are united by a common interest or passion, the rights of the minority are in danger. What motives are to restrain them? A prudent regard to the maxim that honesty is the best policy is found by experience to be as little regarded by bodies of men as by individuals. Respect for character is always diminished in proportion to the number among whom the blame or praise is to be divided. Conscience, the only remaining tie, is known to be inadequate in individuals: In large numbers, little is to be expected from it. Besides, Religion itself may become a motive to persecution & oppression. — These observations are verified by the Histories of every Country antient & modern. In Greece & Rome the rich & poor, the creditors & debtors, as well as the patricians & plebians alternately oppressed each other with equal unmercifulness. What a source of oppression was the relation between the parent cities of Rome, Athens & Carthage, & their respective provinces: the former possessing the power, & the latter being sufficiently distinguished to be separate objects of it? Why was America so justly apprehensive of Parliamentary injustice? Because G. Britain had a separate interest real or supposed, & if her authority had been admitted, could have pursued that interest at our expence. We have seen the mere distinction of colour made in the most enlightened period of time, a ground of the most oppressive dominion ever exercised by man over man. What has been the source of those unjust laws complained of among ourselves? Has it not been the real or supposed interest of the major number? Debtors have defrauded their creditors. The landed interest has borne hard on the mercantile interest. The Holders of one species of property have thrown a disproportion of taxes on the holders of another species. The lesson we are to draw from the whole is that where a majority are united by a common sentiment, and have an opportunity, the rights of the minor party become insecure. In a Republican Govt. the Majority if united have always an opportunity. The only remedy is to enlarge the sphere, & thereby divide the community into so great a number of interests & parties, that in the 1st. place a majority will not be likely at the same moment to have a common interest separate from that of the whole or of the minority; and in the 2d. place, that in case they shd. have such an interest, they may not be apt to unite in the pursuit of it. It was incumbent on us then to try this remedy, and with that view to frame a republican system on such a scale & in such a form as will controul all the evils wch. have been experienced.