It is well known that the names of the seven days of the week are derived from the names of the planets,(54) and it is equally well known that in Europe the system of weeks and week-days is comparatively of very modern origin. It was not a Greek, nor a Roman, nor a Hindu, but a Jewish or Babylonian invention. The Sabbath (Sabbata) was known and kept at Rome in the first century B. C. with many superstitious practices. It is mentioned by Horace, Ovid, Tibullus (_dies Saturni_), Persius, Juvenal. Ovid calls it a day “_rebus minus apta gerendis_.” Augustus (Suet. “Aug.” c. 76) evidently imagined that the Jews fasted on their Sabbath, for he said, “Not even a Jew keeps the fast of the Sabbath so strictly as I have kept this day.” In fact, Josephus (“Contra Apion.” ii. 39) was able to say that there was no town, Greek or not Greek, where the custom observing the seventh day had not spread.(55) It is curious that we find the seventh day, the Sabbath, even under its new Pagan name, as _dies Saturni_ or _Kronike_, mentioned by Roman and Greek writers, before the names of the other days of the week made their appearance. Tibullus speaks of the day of Saturn, _dies Saturni_; Julius Frontinus (under Nerva, 96-98) says that Vespasian attacked the Jews on the day of Saturn, _dies Saturni_; and Justin Martyr (died 165) states that Christ was crucified the day before the day of Kronos, and appeared to his disciples the day after the day of Kronos. He does not use the names of Friday and Sunday. Sunday, as _dies Solis_, is mentioned by Justin Martyr (“Apolog.” i. 67), and by Tertullian (died 220), the usual name of that day amongst Christians being the Lord’s-day, Κυριακή, _dominica_ or _dominicus_. Clemens of Alexandria (died 220) seems to have been the first who used the names of Wednesday and Friday, Ἑρμοῦ καὶ Ἀφροδίτης ἡμέρα. It is generally stated, on the authority of Cassius Dio, that the system of counting by weeks and weekdays was first introduced in Egypt, and that at his time, early in the third century, the Romans had adopted it, though but recently. Be this as it may, it would seem that, if Tibullus could use the name of _dies Saturni_ for Saturday, the whole system of weekdays must have been settled and known at Rome in his time. Cassius Dio tells us that the names were assigned to each day διὰ τεσσάρων, by fours; or by giving the first hour of the week to Saturn, then giving one hour to each planet in succession, till the twenty-fifth hour became again the first of the next day. Both systems lead to the same result, as will be seen from the following table:—