President Abraham Lincoln instituted the celebration of Thanksgiving as a national holiday in 1863 after the Union victory at the battle of Gettysburg, during the American Civil War. It was not a new idea – in 1789, President George Washington had proposed a yearly presidential proclamation of each annual Thanksgiving holiday, but President Thomas Jefferson refused to issue one after he was elected, as he considered it a religious event. Later presidents followed his example, and the holiday was effectively discontinued on the national level until Lincoln’s declaration.

Today, Thanksgiving Day has come to be celebrated every year on the fourth Thursday of November. As a specialist in Catholic history and worship, I am aware that behind the history and legend of the first Thanksgiving lies a rich story that illuminates the medieval Christian roots of the holiday.

Since the beginning of Christianity, the Eucharist, also called Holy Communion or the Lord’s Supper, has been the primary worship service for Christians all over the world. The name itself comes from the ancient Greek word for thanksgiving, “eucharistia,” although in part of the New Testament it is also called “the breaking of bread.”

The service came to be called the Mass in Western Europe, derived from the Latin dismissal rite at the conclusion of the ceremony: Ite missa est – “Go, it is the dismissal.” The term is still used by Roman Catholics today.

One of the most important medieval Catholic rituals, the Eucharist involves a special blessing, called a consecration, of bread and wine. This consecration is rooted in what Jesus Christ did during the ritual meal he shared with his apostles before his arrest and crucifixion – the Last Supper. The ritual as a whole is a thanksgiving to God for the offer of salvation from sin in the crucifixion and resurrection of Jesus Christ. From at least the fourth century, Christians were expected to attend Mass every Sunday, with a few exceptions, and to rest from work.

But Catholics expressed thanksgiving in other ways, too. One hymn’s first line, “Te deum” – which says, “You, God, we praise” – has been used for centuries in Catholic worship, frequently on occasions calling for celebration and thanksgiving.

Legend has it that the text was composed by St. Ambrose, a famous theologian and Doctor of the Church. It is sometimes referred to as the “Ambrosian hymn” in medieval sources.

An early reference to the hymn is in a sixth-century book, “The Rule of St. Benedict,” a collection of regulations for monks and nuns. It is listed as one of the prayers to be recited or sung at Matins, their daily morning communal prayer service.

The Te Deum was often followed by another short hymn: “Non nobis Domine.” Taken from the first line of Psalm 115, “Not to us, Lord, not to us but to your name give glory,” it is another brief expression of thanksgiving to God for whatever event was being celebrated.

Catholics sang the Te Deum as a private or public way to offer thanks to God in a number of situations for centuries. King Philip II of Spain, a devout Catholic, ordered it sung after hearing of the victory of a Catholic fleet against the Ottoman Turks at sea off the shore of Greece. This Battle of Lepanto in 1571 stopped a Muslim advance into Catholic Europe.

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