In the wake of the 2008 financial crisis, architecture found itself back at the drafting table. Clients got spooked (or went broke), construction rates plummeted in the United States and Europe, and young architects in particular had to find new ways to work. And so this past decade has greeted a welter of digital projects, performances, pop-up designs and “paper architecture,” by practitioners born too late for big budgets.

These young architects are heirs to a deep tradition of architecture beyond building — and right now they can discover one of the greatest paper architects of a time before AutoCAD. Jean-Jacques Lequeu, more than two centuries ago, also saw his career upended by political shifts and economic crises: in his case, the French Revolution and the Napoleonic Wars. He, too, had to settle for a career of diminished scope, grinding out maps and renderings for a land registry office and other bureaucracies.

But after hours, alone in his little Parisian bolt-hole, Lequeu (1757—1826) birthed on paper an architecture of wild grandiosity. Styles collided. Historical epochs blended together. European forms mingled with those of Asia and the Middle East. Classical restraint gave way to sensuous, sometimes racy ornament. Buildings became enmeshed with bodies: sometimes human ones, sometimes those of giant farm animals.

Nearly 60 of his voluptuous, perfectionist pen-and-wash drawings (out of some 800) have traveled from the National Library of France for “Jean-Jacques Lequeu: Visionary Architect,” a bewitching exhibition at the Morgan Library & Museum. (The show follows a larger show at the Petit Palais in Paris; another version was seen last year at the Menil Drawing Institute in Houston.) These painstaking sheets, capricious or perverse, steeped in powder blue and misty rose, are a remarkable achievement of the later Enlightenment — and yet they have much more to offer young architects today than a drawing lesson. When the building contracts dry up, you realize your one true client is desire.