Julius Cæsar, 102-44 B.C., instituted a reform of the calendar. This was very much needed, as the Romans were eighty-five days out of their reckoning, and the date for the spring equinox, instead of coming at the proper time, was falling in the middle of winter. An Alexandrian astronomer (Sosigenes) assisted in establishing the new (Julian) calendar. The principle followed was based on ancient Egyptian practice. Among the 365 days of the year was to be inserted, or intercalated, every fourth year an extra day. This the Romans did by giving to two days in leap-year the same name; thus the sixth day before the first of March was repeated, and leap-year was known as a bissextile year. Cæsar, trained himself in the Greek learning and known to his contemporaries as a writer on mathematics and astronomy, also planned a survey of the Empire, which was finally carried into execution by Augustus. There is evidence that the need of technically trained men became more and more pressing as the Empire developed. At first there were no special teachers or schools. Later we find mention of teachers of architecture and mechanics. Then the State came to provide classrooms for technical instruction and to pay the salaries of the teachers. Finally, in the fourth century A.D., further measures were adopted by the State. The Emperor Constantine writes to one of his officials: "We need as many engineers as possible. Since the supply is small, induce to begin this study youths of about eighteen years of age who are already acquainted with the sciences required in a general education. Relieve their parents from the payment of taxes, and furnish the students with ample means."