Apokries (Carnival) are called the three weeks before Clean Monday which is also the first day of the Great Lent. The period of Apokries is associated with the Orthodox tradition of Triodion, which is a movable feast that lasts from the Sunday of the Publican and the Pharisee until the Cheesefare Sunday (Tyrini Sunday).
The Greek carnival has its roots in ancient Greece and is associated with the worship of Dionysus, the god of wine and festivities.
The word carnival comes, etymologically, from the Latin words: carne (meat) and levare (take away, remove, lift), carnem levare, which means a period without meat.
The most likely origin of the Apokries is that it comes from the pagan rituals of the ancient Greeks and the festivals in honor of Dionysus, god of wine and cheerfulness. Also, from the merging of customs that have existed since the ancient times and are related to the regeneration of nature.
These rituals were always celebrated and experienced vigorously and dynamically by the Greeks. People disguised themselves as satyrs or wore festive masks, hurrying into the streets and neighborhoods with bold phrases and actions.
The carnival tradition spread to other parts of the world through the Roman Empire and the discovery of the New World.
These pagan practices were so deeply rooted, however, that they were not completely abolished. When Christianity emerged, although people stopped worshipping the gods of Olympus, the ancient Greek customs to disguise oneself and celebrate in the streets remained.
In almost all regions of Greece, carnival was celebrated in the same way, with minor differences or variations from region to region… (source: agiameteora.net)