Named for mathematician Joseph Stephen Harrison, this fairly prosaic four-story brick building, erected in 1893, was constructed and ornamented according to its namesake's exact specifications. Originally, it housed only the offices and classrooms of the Department of Mathematics, but since Harrison's death, that department has been forced to share with the Department of History, the Department of Medieval and Renaissance Studies, and the Department of Education. Though this has left the building somewhat cramped, the departments involved are relatively small, so their existence is fairly harmonious.

The building's most notable features are the strange geometric patterns and sequences found on the building's façade and the walls of its interior corridors. Over the years, countless math buffs, ranging from the greenest freshmen to some of the greatest minds in the world, have attempted to discover the patterns' true significance. So far, even the best and brightest have succeeded only in determining that the patterns and sequences do indeed represent some kind of coherent code or cipher. Though most respectable mathematicians assume that Harrison probably just did this for his own amusement, probably encoding his own journal, a few philosophical musings or even an elaborate joke, many of Greyson's students and alumni continue to claim that the patterns actually represent secret magical or scientific formulae describing everything from new technological advancements to the secret of eternal life. Until someone actually finds a way to crack the code, however, there's simply no way of knowing.