Historians have represented this intention as the perverse delirium of an unbridled sensuality.  It was certainly the gross act of a madman, but there was perhaps more politics in his madness than perversity; for it was an attempt to introduce into Rome the dynastic marriages between brothers and sisters which had been the constant tradition of the Ptolemies and the Pharaohs of Egypt.  This oriental custom certainly seems a horrible aberration to us, who have been educated according to the strict and austere doctrines of Christianity, which, inheriting in these matters the fine flower of Greco-Latin ideas, has purified and rendered them more rigorous.  But for centuries in Egypt,—­that is, in the most ancient of the Mediterranean civilizations,—­this horrible aberration was looked upon as a sovereign privilege which brought the royal dynasty into relationship with the gods.  By means of it, this family preserved the semi-divine purity of its blood; and perchance this custom, which had survived up to the fall of the Ptolemies, was only the projection of ideas and customs which in most ancient times had had a much wider diffusion along the Mediterranean world, for traces of it can be found even in Greek mythology.  For were not Jupiter and Juno, who constituted the august Olympian couple, at the same time also brother and sister?  Gradually restricted through the spreading of Greek civilization, this custom was finally eradicated at the shores of the Mediterranean by Rome after the destruction of the kingdom of the Ptolemies.

The lunatic Caligula now suddenly took it into his head to transplant this custom to Rome—­to transplant it with all the religious pomp of the Egyptian monarchy, and thus transform the family of Augustus, which up to the present had been merely the most eminent family of the Roman aristocracy, into a dynasty of gods and demigods, whose members were to be united by marriage among themselves in order not to pollute the celestial purity of their blood.  A fraternal and divine pair were to rule at Rome, like another Arsinoe and Ptolemy, whom the Alexandrian throngs had worshiped on the banks of the Nile.  The idea had already matured in his mind at the end of the year 37, and among his three sisters he had already chosen Drusilla to be his wife.  This is proved by a will made at the time of an illness which he contracted in the autumn of the first year of his rule.  In this will he appointed Drusilla heir not only of his goods, but also of his empire, a wild folly from the point of view of Roman ideas, which did not admit women to the government; but it proves that Caligula had already thought and acted like an Egyptian king.

[Illustration:  Remains of the Bridge of Caligula in the Palace of the Caesars.]