First, thanks to everyone who commented and emailed about the sallyport question. I got lots of data and a few good stories. I think the most persuasive take on the matter was provided by the estimable Dr. Keith Cooper, who served as a marshal for a very long time, including a long stint as chief marshal, and thus has had reason to think about these things:

Regarding the Sallyport tradition. I think it arose through the combination of several events. First, we moved Commencement into the Academic Quadrangle and, with Bob Patten’s choreography, began to exit through the Sallyport. (Commencement on the lawn never used the Sallyport. The processions went up the street and down the two sidewalks in the grass of what is now Founder’s Court.). Second, Matriculation in the Grand Hall became too loud, due to the rise of college cheers. Sometime around 1990, Matriculation moved to Founder’s Court. Within a year or two, they moved the post-matriculation reception from the Ray Memorial Courtyard into the Academic Quadrangle, creating a procession inward through the Sallyport. A couple of years later, I started hearing of this “tradition.” Like all traditions, the undergraduates soon believed that it dated back to the founding of the institution.

This makes sense to me. The combination of changes to the commencement and matriculation ceremonies–both going in and coming out–seems to have set it up. Just for fun, here’s commencement in 1985:

And 1986:

One thing I didn’t expect: every correspondent who expressed an opinion about this new tradition didn’t like it. It leaves me cold as well. There’s just absolutely nothing clever about it. As usual, Keith has a very practical analysis:

The “tradition” became a pain in the neck because the student assistants at Commencement would insist on walking around Lovett Hall to take their positions for the recessional. (They needed to be on the Founder’s court side of the building. Both during the walk through and during the ceremony, we would have a majority of the undergraduate helpers who would insist on walking around.) The other nod to this tradition is the fact that we block off the Sallyport before the Friday night Bachelor’s Convocation, to remind them that their degrees have been celebrated, but not yet conferred. Only after conferred on Saturday morning do they walk through the Sallyport. I suspect that fact is largely responsible for the high attendance at Saturday’s Plenary Commencement (along with pressure from Mom).

Bonus: Keith sorting out commencement, 2016.