Many non-Catholics wonder why the Pope and most Catholic clergy wear what resembles to be a yarmulke, the little jewish skullcap eventhough Catholics have probably been wearing skullcaps before it became a popular jewish headgear. To be accurate the Pope does not wear a yarmulke or kippah, but a zucchetto, a name which comes from the Italian expression little gourd, as for the vegetable zucchini, since the hat resembles a small pumpkin cut in half. However, the official Latin name for the Pope’s cap is Pileolus. It is also called Soli Deo, Latin for God alone, to denote that those wearing such hat have consecrated their lives to the Lord.
The skull cap became popular among the Jews, since the XIX century, as the most common form of kippah. The popularization was such that sometimes the skullcap came to have the name ‘Jewish cap’ synonymous with yarmulke. The skullcap is used as a yarmulke in remembrance of divine sovereignty and as a symbol of Jewish cultural identity. There is no standard materials or shape. It is usually made of knitting , silk, velvet or synthetic fabrics and stitched into segments or in one piece.
The Pileolus or Soli Deo became a customary part of the Catholic headgear in the XIII century, when it became widely used by Franciscan Monks; “St. Francis before Honorius III”, painted about 1290 in the upper church of St. Francis at Assisi. It is seen also under the tiara in the effigy on the tomb of Clement VI (d. 1352) at La Chaise-Dieu. The figures on the several tombs of bishops of the fifteenth century in the Roman churches show the zucchetto under the mitre. In the “Ordo” of Jacobus Gajetanus (about 1311) the zucchetto is mentioned in connection with the hat of the cardinals (cap. cxviii), and with the mitre in the “Ordo” of Petrus Amelii (cap. cxliv.), which appeared about 1400.
According to Catholic hierarchy, different color pileolus denote different status within the Catholic clergy, thus the Pope wears a white zuccheto, cardinals wear red ones, bishops wear purple and priests wear black zucchetos. This tradition dates back to the old testament, in which jewish priests were required to cover their heads in the presence of God as a sign of humility. Moreover, all clerics who have episcopal character retain the skullcap for most of the mass, removing it at the beginning of the canon by placing it on completion of the fellowship. The other clerics can not use it outside of the liturgy.