The work was huge: 22 meters (72 feet) long by more than 6 meters (20 feet) high, and it took almost two years to complete.
In the mural, de Conciliis depicted scenes of war and peace, which was the first time such scenes had ever been painted in a Catholic church in Italy.
As a result, many people in the Church denounced the work as scandalous, and the issue was hotly debated in journals and newspapers throughout the world.
The controversy was so large, in fact, that in 1965 it led to a private audience between de Conciliis and Pope Paul VI.
Today the Mural of Peace is considered a major work of art in the city of Avellino. After an earthquake damaged it in 1980, it was restored by a team of experts from the Vatican itself.