While this papal honor is fairly new, its origins and significance go back deeply into church history. In the Middle Ages with the rise of the papacy and the expansion of the papal bureaucracy, the pope’s personal attendants acquired a multitude of tasks. At first this was on an ad hoc basis. Someone might ask the pope for a favor and the pope would refer the petition for study to one of his trusted chaplains. As petitions and staff increased, a certain specialization naturally developed and some chaplains would advise in matters of benefices or finance while others might serve as referees in matters involving canon law. This is probably the origin of the prelate clerics of the apostolic chamber and of the auditors (judges) of the Roman Rota, respectively. Few in number during most of the history of the papacy, these groups of prelates began as actual functionaries—notaries, judges, secretaries and personal attendants of the pope—who as their status grew came to be accorded the style of "monsignor."

The title "monsignor" came into ecclesiastical use at the time of the Avignon papacy (1305-1376) when the popes lived in France and papal power and papal bureaucracy reached its apogee. Certain important clerics at the papal court there were then accorded the French secular style of monseigneur or "milord." The title became monsignore in Italian with the return of Pope Gregory XI (1370-1378) to Rome in 1377. At first this lofty title was used only for ecclesiastical grandees like cardinals. But after 1630, when Pope Urban VIII (1623-1644) gave cardinals the title of "eminence," the old style of monsignore went to senior papal officials beneath the rank of cardinal and to any secular prelate (including bishops) entitled to wear the prelate’s dress, the rochet and mantelletta.

In time another group of monsignors grew up inferior to the prelates di mantelletta. These were the prelates di mantellone, who included the papal chamberlains and the papal chaplains. As the Italian suggests, the cloak of the latter was longer. In the hierarchy of jurisdiction in any one spot the ranking prelate wore a short elbow-length cape or mozzetta. Prelates of lower rank—like protonotaries apostolic and domestic prelates—wore a mantelletta or knee-length sleeveless cloak. Prelates of the lowest rank—like papal chamberlains and chaplains—wore a long floor-length cloak or mantellone, a large purple mantle which covered the cassock and reached to the feet. The arms passed through the lateral side openings of this cloak. In this finely-graded system, jurisdiction, actual or notional, determined one’s attire. Thus as choir dress in the sanctuary a cardinal outside Rome, a primate in his region, a metropolitan in his province, and a residential bishop in his diocese wore a mozzetta over his rochet and cassock. In other places (and in all places in the case of an auxiliary bishop) the mantelletta replaced the mozzetta.

The choir cassock of prelates di mantellone was purple with purple trim of a lighter hue. During papal chapels or functions over their purple cassock and purple silk cincture went the mantellone, which was made of wool in winter and of silk in summer. Outside Rome they could add purple socks and a purple tassel on their ecclesiastical hat. During liturgical celebrations they wore a surplice over their purple cassock. Their house dress was a cassock or simar of black with purple buttons, buttonholes and trimmings worn with a purple silk cincture. Their ferraiolone, or cloak, was of plain black silk. Their biretta was of silk and lined with purple taffeta but otherwise it was entirely black like that of a simple priest.

The first type of these lesser monsignors, the papal chamberlains, had provided the pope’s ecclesiastical retinue. The papal chamberlains were divided into four grades, participating, supernumerary, nonorary chamberlains in purple attire, and honorary chamberlains extra urbem.

From the days of Pope Leo the Great (440-461) the pontifical household had included papal chamberlains who were personal attendants on the pope in his private apartments. The number of papal chamberlains was never large, although their proximity to the pope meant that many chamberlains would enjoy notable ecclesiastical careers and some were even promoted to the sacred purple. Their privileges were considerable. They ranked ex officio as papal Lateran counts, Knights of the Golden Spur, and nobles of Rome and Avignon.

In time, to honor a distinguished ecclesiastic, to clothe with an honorable office an ecclesiastic sent abroad on papal business, or simply to augment the splendor of a ceremony by the attendance of a larger retinue, honorary or extraordinary papal chamberlains were created. Some extraordinary chamberlains, moreover, because of the more frequent service they provided in the papal antechamber, had enjoyed the ration of bread and wine that went to the papal familiarius or member of the extended papal family. Out of the class of extras without such a ration grew a new class of more purely honorary chamberlain, the honorary chamberlains in purple attire. Finally, as rulers of the Papal States which before 1870 stretched across central Italy, earlier popes traveled much more than "prisoners of the Vatican" like Leo XIII and Pius X. This fact of life lead Pius VI to create a new class of chamberlain, the honorary chamberlain extra urbem or outside the City, to attend him on his travels. Outside Rome, they dressed in purple like other papal chamberlains. But since their service did not extend to Rome, in the City they could not use the style and other privileges of their rank.

Among the clerics of the papal court, the reform found a byzantine maze of some fourteen grades of monsignori and reduced this complex corps of "milords" to classic simplicity. The Pauline reform found domestic prelates, four kinds of protonotaries apostolic, four varieties of papal chamberlains, and five types of papal chaplains. It left the pontifical clergy divided, like Gaul, into three parts, protonotaries apostolic, honorary prelates of His Holiness, and chaplains of His Holiness. The chamberlains were now a more priestly-sounding category called—more appropriately in an ecclesiastical household—"chaplains of His Holiness."

The accent on the sacramental meant that the sacramental orders of bishop and priest would be stressed rather than the jurisdiction the papal clergy happened to exercise. For this to happen papal prelates had to cease dressing and being addressed like bishops.

Thus, the use of the miter by protonotaries apostolic was prospectively abolished and the use of the rochet (or episcopal surplice) was severely limited to a handful of papal prelates resident in Rome. The upshot was that among the secular clergy the rochet was once again restricted to bishops, and the surplice (again) became the choir vestment of all clerics beneath that order..

At the same time the mozzetta was made the emblem of the episcopal order and now all bishops, diocesan and auxiliary, could wear it and wear it everywhere and not merely within their own jurisdiction as before. Since attire was now grounded in one’s sacramental order, the mantelletta and mantellone, which had been bottomed on the wearer’s jurisdiction, were now superfluous. Hence, except for a handful of papal prelates resident in Rome who retained the mantelletta, these garments were also prospectively suppressed. The mantellone, moreover, being the livery garb of the chamberlains, was essentially secular attire for the retinue of a temporal sovereign. Its abolition thus in addition gave a less secular and more sacred look to the pontifical household.

The sacramental principle had actually been embraced a century earlier when Pius IX and Leo XIII had assigned to bishops the purple skullcap and biretta in order that there might be a well-marked difference between the appearance of bishops and that of simple priests. Paul VI would extend to the clerics of the papal household this policy of assigning specially colored gear to particular sacramental orders. If the purple biretta had become and episcopal ensign, now a black one would become an ensign of the priesthood. Accordingly, almost all clerics of the pontifical household who lacked the episcopal character would henceforth wear a black biretta in token of their priesthood. In this way the entire "priesthood of the second order" would be covered alike.

This nineteenth century pro-episcopal and color-coding policy Paul VI would also extend more rigorously in his reform of the pontifical household. While honorary prelates of His Holiness retained the purple choir cassock, their ordinary attire was their black cassock or simar with red trim. Only supernumerary protonotaries apostolic might now wear the purple ferraiolone or cloak of silk. The papal chamberlains had been the retinue of the popes as secular rulers and for them purple was a livery color. Now, to stress their presbyteral order rather than this secular function their purple cassock was abolished. Instead, after the reform, with marked simplicity papal chaplains would wear more priestly garb, the traditional ensign of clerics, the black cassock. Henceforth, on all occasions their old house cassock, which was black with purple buttons, buttonholes and trimmings, and a purple silk cincture would serve sufficiently to mark them off at once as priests and as chaplains of His Holiness. For choir dress, like other priests, they would don a surplice over their cassock as they ever had.

The same aim was evident in the reformed styles of address for clerics of the pontifical household. The reform did away with superlatives like "Right Reverend" and "Very Reverend for honorary prelates. Henceforth, the superlative form of address became an exclusively episcopal prerogative among secular clerics. In the future with but a few exceptions, "Reverend Monsignor" became the sole style of address for clerics of the pontifical household, the "Reverend" betokening their priesthood and the "Monsignor" marking—as it had since the days in Avignon—their membership in the pontifical household.