Why they cast lots for it, next appears: They said therefore among themselves, Let us not rend it, but cast lots for it whose it should be. It seems then that the other garments were made up of equal parts, as it was not necessary to rend them; the tunic only having to be rent in order to give each an equal share of it; to avoid which they preferred casting lots for it, and one having it all. This answered to the prophecy: That the Scripture might be fulfilled which saith, They parted My raiment among them, and for My vesture they did cast lots.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Tract. cxviii