Definition of "long robe"

[H]e contracted intimacies in some families of good fashion, especially those of the long robe, which would have enabled him to pass his time very agreeably, had he been a little easier in point of fortune […] .

1751, [Tobias] Smollett, The Adventures of Peregrine Pickle […], volumes (please specify |volume=I to IV), London: Harrison and Co., […]

I once saw two brothers of the long robe involuntarily stop and heartily enjoy the dialogue of that merry little fellow with Jack Ketch, who was about to hang Punch for the murder of his wife and his innocent babe.

1828, JT Smith, Nollekens and His Times, Century Hutchinson, published 1986, page 150