what is the historical development of the wearing of the royal arch robes by the principals

By 1765, early records of the Excellent, Grand and Royal Chapter show that the three Principals—Zerubbabel, Haggai, and Joshua—wore robes, caps, and jewels during ceremonies, as a paper read before Quatuor Coronati Lodge records. These early practices explicitly omitted aprons for officers who wore robes. The 1765 By-Laws of Grand Chapter codified this distinction, specifying that all Companions were to wear aprons except those officers who were appointed to wear robes.

The use of ceremonial vestments expanded further the following year. In 1766, Grand Chapter ordered three white surplices for the three Sojourners to wear during Chapter work, establishing a clear visual distinction between the candidate, the companions, and the robed officers, as shown in the same paper read before Quatuor Coronati Lodge.