2. A second indication of the hold which education had upon the age is the fact that teaching had come to be a recognized and lucrative profession. This is shown not so much by the instances of individual teachers,[37] who might be regarded as exceptional, as by the fact of the recognition of teachers by the State and by municipalities. The recognition by the State took the double form of endowment and of immunities from public burdens. (_a_) Endowments probably began with Vespasian, who endowed teachers of Rhetoric at Rome with an annual grant of 100,000 sesterces from the imperial treasury. Hadrian founded an Athenæum or University at Rome, like the Museum or University at Alexandria, with an adequate income, and with a building of sufficient importance to be sometimes used as a Senate-house. He also gave large sums to the professors at Athens: in this he was followed by Antoninus Pius: but the first permanent endowment at Athens seems to have been that of Marcus Aurelius, who founded two chairs in each of the four great philosophical schools of Athens, the Academic, the Peripatetic, the Epicurean, and the Stoic, and added one of the new or literary Rhetoric, and one of the old or forensic Rhetoric.[38] (_b_) The immunities of the teaching classes began with Julius Cæsar, and appear to have been so amply recognized in the early empire that Antoninus Pius placed them upon a footing which at once established and limited them. He enacted that small cities might place upon the free list five physicians, three teachers of rhetoric, and three of literature; that assize towns might so place seven physicians, three teachers of rhetoric, and three of literature; and that metropolitan cities might so place ten physicians, five teachers of rhetoric, and five of literature; but that these numbers should not be exceeded. These immunities were a form of indirect endowment.[39] They exempted those whom they affected from all the burdens which tended in the later empire to impoverish the middle and upper classes. They were consequently equivalent to the gift from the municipality of a considerable annual income.