Regarded by his contemporaries and later commentators until the early twentieth century art as the maximum result by Guercino, the huge altarpiece of the Burial of Holy Petronilla - the painting of the legendary daughter of Peter measuring more than 7x4 meters - was commissioned for an altar of St. Peter’s Basilica, from where it was removed in 1730 to be replaced by a copy in mosaic of Pietro Paolo Cristofari and is currently on display in the Capitoline Museums.
Calvi also writes that "this commitment and emulation would add to him the stimulus or light that drew from the sight of so many egregious paintings adorning Rome, Guercino seemed to go beyond himself and was studying the make his style even more valuable and surprising since, beyond the judicious discovery and grandeur of well-arranged parts, as well as the design and adjusted the contrast of shadows and lights, he expressed more precisely the heads and ends, he painted with live and soft real meat batter and he gave so much harmony and lots of height to the colors, and for the strength and for the relief he does not seem to be able to go further; and this is what some call his second manner, which earned him to be entitled by amateur strangers to the title of Magician of Italian painting."
The ones that appeared to be the best work qualities are modernly subject to criticism: the academic values of fairness and accuracy are seen as expression of less sincerity and originality. Guercino retains its typical lozenge composition "but the link of the picture is already more loose, more overload, less necessary than in previous canvases, the bright party lost the transparency of San Guglielmo or the sense of black and white in the Aurora to weight the gradient; everything got worse, from architecture to the wings of angels, to the palette that is not tonal but chromatic, with those showy wealth. Guercino has lost here its good, measured taste [...]."
He painted a few other paintings in Rome: a large painting on the ceiling of San Crisogono in Trastevere commissioned by Cardinal Scipione Borghese - now in London - and Mary Magdalene in the homonym church at Course. With the death of Pope Gregory XV on July 8, 1623 – of whom we keep the portrait by Guercino – he has no longer the possibility to carry out the planned great decoration in St. Peter’s, for which he had been promised 22,000 crowns, and Guercino at the end of the month took its way back in Cento.