A ‘canto’ is a major division of an epic or long narrative poem, and in this instance, ‘Canto 19’ relates to one of the most important works in medieval literature, namely Dante’s ‘The Divine Comedy’ (written in 1320).
The Divine Comedy follows Dante himself, as he embarks on an imaginary journey through Hell (Inferno), Purgatory (a place or state of punishment wherein the souls of those who die may expiate past sins, via suffering, and so become fit for heaven) and Paradise (Heaven).
‘Inferno: Canto 19’ describes the third ditch in the eighth circle of Hell, which is dedicated to those who committed the sin of simony (the sin of attempting to exchange money or favours for power or positions in the Christian church).
At this point in the narrative, Dante (alongside his guide Virgil) reaches the top of a ridge. He looks down into a valley of rocks below, and the rocks are covered in round holes in the ground. Dante sees that there are people stuffed head-first into these holes with their feet sticking out of the top, the soles of which are on fire!