By admission of an introductory plaque at “Roman Sketches,” the rough impressions inside a sketchbook are not meant for the public eye. Raw material and impressionistic input, they are more Snapchat than Ansel Adams, but there’s something alluring about sketches in their revealing, almost crude simplicity.

Alexander Purves’ ’58 ARC ’65 sketches of Rome are no exception. Purves, professor emeritus at the School of Architecture, has spent four weeks in Rome each of the last 12 summers leading an intensive drawing course for architecture graduate students. Over those months, he’s amassed 12 individual sketchbooks filled with his jotted interpretations of the city, a small selection of which have been chosen for display in an exhibit running until June at the Whitney Humanities Center. From delicate watercolors to spectral outlines of the Piazza Popolo, each work offers a moment from Purves’ tours of the city.

Similar to the paradox of displaying an artist’s private sketches is that of recreating one of the world’s great cities in a series of miniature line drawings. Black and white impressions wouldn’t seem adequate to represent Rome’s splendor, yet Purves’ trained eye makes virtue of constraint. Using almost exclusively ballpoint pen, a testament to his self-professed “obsession” with line drawing, Purves’ shading consists of scribbles varying in intensity from light to apocalyptic. Yet his drawings of St. Peter’s Basilica lose nothing of its looming grandeur, and in fact the minimalism of his medium reduces the ornate building to its imposing silhouette, a stark and almost imperial shape.

It takes Purves few lines to capture a building. He seems to forsake detail for overall form, and although this is the nature of a sketch, those of more impressive buildings tend even further from intricacy. “If you want to know a building, you should draw it,” he says, and his sketches are certainly not those of an awed tourist but of a practiced eye. Many emphasize architectural features of a structure, such as a series looking up at the tower of St. Ivo or a view inside St. Peter’s of the Basilica’s towering arches. Still, other sketches actually have measurements and markings on them, while others attempt to translate a building into a blueprint. It’s worth remembering that these drawings were not for pleasure, but for business — Purves sketched them while leading a group of students, some of whom appear in the sketches — and there is certainly a functional aspect to the work, much of which examines geometric shapes both intricate and simple within the architecture.

But there is a fleeting quality to some of the work as well, as if seen from a moving car’s window or noticed briefly in passing. Two views of the tower at St. Ivo retain that same transient feel even though one is a watercolor and another a line drawing; both depict the rush of cars and pedestrians surrounding the 16th century church, and Purves’ familiarity with the locale seems obvious. Yet neither the routine of the city nor the rapidity of his pencil strokes can fully obscure the simple elegance of the church, which Purves paints in the glow of early evening.

In other pictures, though, Purves’ artistic side dominates. Some are details of columns or fine carvings on medieval buildings such as Santa Costanza, a fourth century church. These don’t have the brevity of the broader, architectural works, but instead demonstrate Purves’ sleight of hand with his preferred ballpoint. Despite or even because of this, they lack the immediacy of the Basilica of the Piazza Sant’Ignazio, which seem to impress upon us exactly what Purves saw as he sketched.

Displaying sketches like these creates an interesting artistic conundrum. Many of Rome’s buildings are art in themselves, designed to instill viewers and patrons with a sense of awe or spiritual presence. Yet a sketch of these artistic achievements is, by the artist’s own admission, not meant as a work of art in itself. Many of Purves’ sketches appear more functional than artistic. And yet wander over to the Whitney Humanities Center and there they hang, worthy of display. In effect, what Purves accomplished in his rough drawings of Rome’s breathtaking architecture was to take art and turn it into not-art, but there is certainly something exciting and immediate about the sketches on display.

The Whitney Humanities Center has rightly turned those sketches into art again. Purves’ works capture Rome in short but powerful glances. His acquaintance with its monuments and the limitations of his sketchbook make for a striking exhibition.