The "Eiresioni" roamed the streets of Athens on the seventh day of the Pyanopsia, a festival in honor of the god Apollo (14 October - 12 November) by children who sang carols from house to house, taking a tip from the landlord or the lady.

When the children arrived at their own houses, they hung the "Eiresioni" over their front door, where it stayed until the same day of the following year, when, after placing the new one, they took down the old one and burned it.

During the ritual, a young man pure over the branch with wine from a ceremonial amphora and hung it on the gate of the temple of Apollo.

This gesture was an expression of thanks for the fertility of the year that was ending and a request for continued fertility in the following year.

Eiresioni was dedicated to Athena, Apollo, the Sun and the Hours (Eunomia, Dikis and Eirini).

According to tradition, the custom was established by Theseus, when he set out for Crete to kill the Minotaur. Then, he stopped in Delos, where he made a sacrifice to Apollo, saying that if he won the battle with the Minotaur, he would offer him decorated olive branches to thank him. Returning to his homeland, Theseus fulfilled his promise by establishing the institution of the "Eiresioni".

The theocratic regime of Byzantium condemned the custom as idolatrous and forbade its performance.

However, the Greeks who traveled a lot passed it on to the Northern peoples, who, due to the lack of olive trees, decorated branches from the trees that grew in their regions, such as fir trees.

Centuries later, the first Christmas tree in Greece was decorated by the Bavarian King Otto in 1833 at the palace of Nafplion and the Greeks, from the historical memory of "Eiresioni", quickly adopted the Christmas tree with the fir tree (and cypress in some places), slowly replacing the traditional decoration of the ship.