Christian Lore

In the Hebrew scriptures, the swan is mentioned as being unclean, not suitable for human consumption. (Lev. 11:18; Deut. 14:16)

In Christian lore, the swan is sacred to the Virgin Mary. Its swan song represents the resignation of the martyrs. The constellation Cygnus was called the Northern Cross at least from the time of Bede, and symbolized the Cross of Calvary.

Constantine

In Hoc Signo

The Roman Emperor Constantine I began the process of making Christianity the official religion of the Roman Empire. According to legend, he saw a sign in the sky before the Battle of Milvian Bridge in 312 CE. The sign he saw was traditionally said to have been the Chi-Rho, with the Greek words Εν Τουτω Νικα (By this, conquer); in Latin, “In hoc signo vinces” (By this sign you will conquer). He won the battle and became sole Emperor of Rome. He attributed his victory to the Christian God, and set about transforming the pagan religion of Sol Invictus (the Unconquered Sun) into Christianity.

It has been suggested that Constantine saw a conjunction of the planets Mars, Saturn, Jupiter and Venus in the constellations Capricorn and Sagittarius, forming a Chi-Rho pattern. Such an event would (according to the theory) have had an unfavorable meaning astrologically, and undermined the morale of Constantine’s pagan army. Therefore, Constantine gave the event a Christian interpretation.

Some historians suggest Constantine saw a cross, not a Chi-Rho. It has been suggested that he saw Cygnus, the Northern Cross. On the evening of 26 or 27 October 312 Cygnus would have been still near its high point in the sky. The words “in hoc signo vinces” (by this sign you will conquer) would then have been a pun doubling on “in hoc cygno vinces” (by this swan (that is, a cross) you will conquer). In Latin, cygnus is pronounced with a hard k, which minimizes but does not eliminate the pun.