Charles Monnet chose an unusual subject, or rather a subject not especially favoured by his contemporaries, for this work: the procession held to mark Lent in 1758. Thus we are looking at an actual event, yet an event in which the artist skilfully combines his narrative composition with portraiture. The portrait is that of Cardinal Antonio Andrea Galli, depicted 

as he processes on his black horse towards the Quirinale Palace. The podium bears a 16th century inscription (dating back to the time of Pope Sixtus V, yet reiterating its now lost but abundantly quoted Classical predecessor) identifying the colossal statue as OPUS PHIDIAE, a Roman copy of a bronze group depicting the Dioscuri, Castor and Pollux. Interpreted as the sons of Zeus, they enjoyed particular prestige in Rome because they had always come to the Romans's aid in battle.

Pope Benedict XIV raised Antonio Galli to the rank of cardinal on 26 November 1753, appointing him titular cardinal of Sant'Alessio, although this was changed to San Pietro in Vincoli, a basilica closer to his heart, in 1757. In the years prior to his nomination, Galli had made a name for himself with his positions on issues of both a theological and a practical nature. He was appointed advisor to the Sacred Congregation of the Index in 1736, while in 1740 he became a member of the Liturgical Academy and of the Congregation for the Reform of the Breviary, a project on which he was to work for the whole of his life.

The pope subsequently called on his newly appointed cardinal to concern himself with a far broader range of issues. In December 1753 he made him a member of the Congregation of the Holy Office (or Congregation for the Doctrine of the Faith), of the Sacred Congregation of the Index (whose prefect he was also to become), of the Rituals and of the Examination of Bishops, while the following year he appointed him to the Sacred Congregation of Indulgences and Holy Relics. Galli joined the Apostolic Penitentiary, the oldest ministry and the first of the Roman Curia's tribunals, in June 1755. The post of Major Penitentiary (which Galli was to hold until his death) gave a cardinal the power to impose sanctions and to grant dispensations, absolution and commutations to the clergy.