The Babylonian system was received by the Greeks in the 4th century BC (notably via Eudoxus of Cnidus). However the designation of the seven days of the week to the seven planets is an innovation introduced in the time of Augustus. The astrological concept of planetary hours is rather an original innovation of Hellenistic astrology, probably first conceived in the 2nd century BC. The seven-day week was widely known throughout the Roman Empire by the 1st century AD, along with references to the Jewish Sabbath by Roman authors such as Seneca and Ovid. When the seven-day week came into use in Rome during the early imperial period, it did not immediately replace the older eight-day nundinal system. The nundinal system had probably fallen out of use by the time Emperor Constantine adopted the seven-day week for official use in CE 321, making the Day of the Sun () a legal holiday. The earliest evidence of an astrological significance of a seven-day period is connected to Gudea, priest-king of Lagash in Sumer during the Gutian dynasty, who built a seven-room temple, which he dedicated with a seven-day festival. In the flood story of the Assyro-Babylonian epic of Gilgamesh, the storm lasts for seven days, the dove is sent out after seven days, and the Noah-like character of Utnapishtim leaves the ark seven days after it reaches firm ground. It is possible that the Hebrew seven-day week is based on the Babylonian tradition, although going through certain adaptations. George Aaron Barton speculated that the seven-day creation account of Genesis is connected to the Babylonian creation epic, Enûma Eliš, which is recorded on seven tablets. Counting from the new moon, the Babylonians celebrated the 7th, 14th, 21st and 28th as "holy-days", also called "evil days" (meaning "unsuitable" for prohibited activities). On these days, officials were prohibited from various activities and common men were forbidden to "make a wish", and at least the 28th was known as a "rest-day". On each of them, offerings were made to a different god and goddess. In a frequently-quoted suggestion going back to the early 20th century, the Hebrew "Sabbath" is compared to the Sumerian "sa-bat" "mid-rest", a term for the full moon. The Sumerian term has been reconstructed as rendered "Sapattum" or "Sabattum" in Babylonian, possibly present in the lost fifth tablet of the Enûma Eliš, tentatively reconstructed "[Sa]bbath shalt thou then encounter, mid[month]ly".