Christ was born in the time of Emperor Augustus, although a probable error of four years in relation to the official chronology. In early, Christianity was unnoticed in Rome, confused with Judaism and its various sects, but it had then a remarkable success for expansion to become the official religion and finish the traditional pagan religion off.
Christianity, in reality a syncretism (gr. συγκρητισμός, the combining of different beliefsis), collects beliefs, moral principles, rituals, iconography, of the various parts of the Roman Empire, where it is introduced, and integrates them into a more or less coherent unit. It is known, for example, how everywhere, on the ruins of pagan temples are built Christian churches or natural places such as forests, caves, mountains, with high religious value, continue the tradition under the support of an Christian image or symbol.
Therefore it is still curious that the names of the days of the week remain “pagans” throughout the West, bearing the name of the stars that the ancients knew.
In Latin Monday is the day of the Moon (dies lunae), Tuesday the day of the god Mars (dies Martis), Wednesday day of Mercury (Mercurii dies), Thursday day of Jupiter (Dies Iovis), Friday the day of Venus (Veneris dies ). Just got changed and not everywhere Saturni Dies (Saturn day),Saturday, replaced by Jewish Sabbaht and Dies Solis, the day of the Sun, changed or Dominicum or Dies Dominica, Sunday (Lord's Day). But as I said, not everywhere, in English remain still Saturday (Saturn's day) and Sunday (day of the Sun). With the remaining days in English or German with them were also unsuccessful in converting task, Montag is the day of the moon and Sontag is the day of the sun.
This process is even more curious when we remember that in early the Romans did not know the "week" or seven-day as time unit like us. This is shown by its month distribution iinto three periods called Kalends (the 1st of each month), Nones (the 5th in a few months and 7th others) e Ides (the 13th day in a few months and 15th in others).
The week is originally a Babylonian creation later adopted by the Jews. There was widespread in Rome in imperial times and imposed in the year 321 by the Emperor Constantine. Naturally the rest day was not the Jewish Sabbath but "Solis dies = day of the Sun" Christianized "Domenica Dies = Sunday or day of the Sun", as stated.