The date was decided in honor of the birthday of Leonardo da Vinci. Da Vinci was chosen as a symbol of world peace, freedom of expression, tolerance, brotherhood and multiculturalism as well as art’s importance to other fields.

The Universal Day of Culture under the Banner of Peace, known also as the World Day of Culture, is an observance held annually on April 15 in many countries around the World to promote the protection of culture, the Roerich Pact and the Banner of Peace. World Art Day is an international celebration of the fine arts which was declared by the International Association of Art (IAA) in order to promote awareness of creative activity worldwide.

Links:
World Art Day

Universal Day of Culture

The International Movement for the affirmation of April 15 as Universal Day of Culture