History of the Sabbath and First Day of the Week - John N. Andrews

Origen, Cyprian, Anatolius, Commodianus,
Victorinus, and Peter of Alexandria, can be
adduced, who give this name to Sunday.
No one of these fathers ever claims for this title
any apostolic authority; and it has been already
shown that they could not have believed the day to
be the Lord’s Day by divine appointment. So far,
therefore, is the use of this term by these persons as
a name for Sunday from conflicting with the
statement that Sylvester, by his apostolic authority,
established this name as the rightful title of that
day, that it shows the act of Sylvester to be exactly
suited to the circumstances of the case. Indeed,
Nicephorus asserts that Constantine, who
considered himself quite as much the head of the
church as was the pope, "directed that the day
which the Jews considered the first day of the
week, and which the Greeks dedicated to the sun,
should be called the Lord’s Day."[44] The
circumstances of the case render the statements of
Lucius and Nicephorus in the highest degree
probable. They certainly do not indicate that the
pope would deem such act on his part unnecessary.
597