The 1890s (especially the University's 150th anniversary in 1896) saw increasing interest, although it was not until the 1950s that Reunions took on today's level of organization, particularly with respect to on-campus housing for returning alums.
The 25th Reunion class heads the parade; they are led by the Princeton University Band, which plays traditional songs such as Going Back to Nassau Hall.
[5] Classes celebrating a major reunion (multiples of five—5th, 10th, and so on) often wear themed costumes, which have ranged from Roman legionnaires to firefighters and Uncle Sam lookalikes.
[6] Frequently, classes will hire musical groups, such as the Mummers, local high school marching bands, and a calliope, to lead them through the parade.
Some think the University also felt that too many alumni would stop off at their eating clubs on Prospect Avenue before finishing the P-Rade, and so it changed (and shortened) the route so that it does not leave campus.