From card game to oracle
The first tarot decks, the tarocchi, were painted for the courts of northern Italy in the 15th century to play a trick-taking card game. The trump cards, our Major Arcana, were moral and Christian allegories that everyone recognized.
Using the cards for divination came three centuries later: in 1781 Antoine Court de Gébelin linked them to an ancient wisdom, and soon after Etteilla published the first deck designed for reading. Since then, every school has added its own symbols.