[9][10] When Pope Gregory IX waged war against Emperor Frederick II in 1228, papal troops were described by Richard of San Germano as "bearing the sign of the keys" (clavigeros hostes or clavesignati).

[11] The earliest blazoning of the arms of the Holy See is that found in Froissart's Chronicles of 1353, which describes them as "gules two keys in saltire argent".

[13] In 1952–1953 the English Heraldry Society gave the blazon of the arms of the Holy See as "Gules a key or [("gold" or "yellow" in heraldic terminology)] in bend above a key argent [("silver" or "white" in heraldic terminology)] in bend sinister, both wards upwards, the bows united by a cord or, above the shield a tiara, its three crowns or [("gold")], the mitre argent [("silver")]".

By the end of Froissart's 14th century the papal tiara was included in the coat of arms of the Holy See according to Galbreath[2] and Insegne e simboli: araldica pubblica e privata medievale e moderna.

[20][21] Claudio Ceresa says that the oldest known representation of the crossed keys beneath the papal tiara dates from the pontificate of Martin V (1417–1431), whose successor, Eugene IV (1431–1447), included it in the design of a silver coin.

In 1301, Boniface VIII, at that time in conflict with Philip IV of France, added a second crown to indicate that his spiritual authority was superior to any civil power.

In 1342, Benedict XII added a third crown to symbolize the superiority of papal religious authority over that of non-religious monarchs.