But by the side of the king and of the burgess-assembly there appears in the earliest constitution of the community a third original power, not destined for acting like the former or for resolving like the latter, and yet co-ordinate with both and within its own rightful sphere placed over both. This was the council of elders or senatus. Beyond doubt it had its origin in the clan-constitution: the old tradition that in the original Rome the senate was composed of all the heads of households is correct in state-law to this extent, that each of the clans of the later Rome which had not merely migrated thither at a more recent date referred its origin to one of those household-fathers of the primitive city as its ancestor and patriarch. If, as is probable, there was once in Rome or at any rate in Latium a time when, like the state itself, each of its ultimate constituents, that is to say each clan, had virtually a monarchical organization and was under the rule of an elder - whether raised to that position by the choice of the clansmen or of his predecessor, or in virtue of hereditary succession - the senate of that time was nothing but the collective body of these clan-elders, and accordingly an institution independent of the king and of the burgess-assembly; in contradistinction to the latter, which was directly composed of the whole body of the burgesses, it was in some measure a representative assembly of persons acting for the people. Certainly that stage of independence when each clan was virtually a state was surmounted in the Latin stock at an immemorially early period, and the first and perhaps most difficult step towards developing the community out of the clan-organization--the setting aside of the clan-elders - had possibly been taken in Latium long before the foundation of Rome; the Roman clan, as we know it, is without any visible head, and no one of the living clansmen is especially called to represent the common patriarch from whom all the clansmen descend or profess to descend so that even inheritance and guardianship, when they fall by death to the clan, devolve on the clan-members as a whole. Nevertheless the original character of the council of elders bequeathed many and important legal consequences to the Roman senate. To express the matter briefly, the position of the senate as something other and more than a mere state-council - than an assemblage of a number of trusty men whose advice the king found it fitting to obtain - hinged entirely on the fact that it was once an assembly, like that described by Homer, of the princes and rulers of the people sitting for deliberation in a circle round the king. So long as the senate was formed by the aggregate of the heads of clans, the number of the members cannot have been a fixed one, since that of the clans was not so; but in the earliest, perhaps even in pre-Roman, times the number of the members of the council of elders for the community had been fixed without respect to the number of the then existing clans at a hundred, so that the amalgamation of the three primitive communities had in state-law the necessary consequence of an increase of the seats in the senate to what was thenceforth the fixed normal number of three hundred. Moreover the senators were at all times called to sit for life; and if at a later period the lifelong tenure subsisted more de facto than de jure, and the revisions of the senatorial list that took place from time to time afforded an opportunity to remove the unworthy or the unacceptable senator, it can be shown that this arrangement only arose in the course of time. The selection of the senators certainly, after there were no longer heads of clans, lay with the king; but in this selection during the earlier epoch, so long as the people retained a vivid sense of the individuality of the clans, it was probably the rule that, when a senator died, the king should call another experienced and aged man of the same clanship to fill his place. It was only, we may surmise, when the community became more thoroughly amalgamated and inwardly united, that this usage was departed from and the selection of the senators was left entirely to the free judgment of the king, so that he was only regarded as failing in his duty when he omitted to fill up vacancies.
The prerogatives of this council of elders were based on the view that the rule over the community composed of clans rightfully belonged to the collective clan-elders, although in accordance with the monarchical principle of the Romans, which already found so stern an expression in the household, that rule could only be exercised for the time being by one of these elders, namely the king. Every member of the senate accordingly was as such, not in practice but in prerogative, likewise king of the community; and therefore his insignia, though inferior to those of the king, were of a similar character: he wore the red shoe like the king; only that of the king was higher and more handsome than that of the senator. On this ground, moreover, as was already mentioned, the royal power in the Roman community could never be left vacant When the king died, the elders at once took his place and exercised the prerogatives of regal power. According to the immutable principle however that only one can be master at a time, even now it was only one of them that ruled, and such an "interim king" (interrex) was distinguished from the king nominated for life simply in respect to the duration, not in respect to the plenitude, of his authority. The duration of the office of interrex was fixed for the individual holders at not more than five days; it circulated accordingly among the senators on the footing that, until the royal office was again permanently filled up, the temporary holder at the expiry of that term nominated a successor to himself, likewise for five days, agreeably to the order of succession fixed by lot. There was not, as may readily be conceived, any declaration of allegiance to the interrex on the part of the community. Nevertheless the interrex was entitled and bound not merely to perform all the official acts otherwise pertaining to the king, but even to nominate a king for life - with the single exception, that this latter right was not vested in the first who held the office, presumably because the first was regarded as defectively appointed inasmuch as he was not nominated by his predecessor. Thus this assembly of elders was the ultimate holder of the ruling power (imperium) and the divine protection (auspicia) of the Roman commonwealth, and furnished the guarantee for the uninterrupted continuance of that commonwealth and of its monarchical - though not hereditarily monarchical - organization. If therefore this senate subsequently seemed to the Greeks to be an assembly of kings, this was only what was to be expected; it had in fact been such originally.