Guest speakers at the event will be Trócaire’s head of policy and advocacy, Lorna Gold, and the former president of Mater Dei, Fr Dermot Lane.

Archbishop Michael Neary described the artwork and said: “It is difficult to find a language which would capture the beauty and magnificence of what we behold and yet isn’t it just a shadow of the reality which those 15 people looked upon on that August evening at the gable end a few yards away.”

The illustration was done by the renowned Irish artist PJ Lynch and it took 1.5 million pieces to complete the mosaic.

Team of mosaic-makers from Italy are in Knock to assemble Irish artist PJ Lynch's depiction of the 1879 apparition.