From the air, the 46,000 lunging, rolling, curving, tangled miles of America's Interstate Highway System sprawl across the continent like some outsized Rorschach pattern. These multi-laned, guard-rail-clad corridors by now seem timeless, like pre-Cambrian mountains bolted to the landscape. So it's hard to believe that America's freeway system turns 50 this summer — a chronological blip on the tectonic plates too slight for a spectrometer, but in the life of our republic, a golden anniversary.

In truth, the system's true origins do go back at least several more years. As a young lieutenant colonel in 1919, Dwight Eisenhower volunteered to act as an observer on the U.S. Army's first motorized transcontinental convoy. But the 62-day Washington-to-San Francisco trek left him appalled. On the often unpaved, poorly maintained roads that comprised their route, trucks became stuck in mud, disappeared into clouds of dust, and slid on ice; on occasion, they even crashed through the beds of creaky wooden bridges.

Memories of that obstacle course lingered with Eisenhower. And two decades later, as the Supreme Allied Commander in World War II, he noted how easily his armies disrupted German supply-lines by bombing railroads. But he also noticed how, despite Allied pummeling, the country's Autobahn had remained passable. In the 1950s, the general-turned politician, by then elected president, resolved to build a similar system across the United States. "The old convoy," he recalled, "had started me thinking about good, two-lane highways, but Germany had made me see the wisdom of broader ribbons across the land."

Military considerations — his perceived need for good roads to transport troops and materiel over far-flung continental distances — initially compelled Eisenhower. But, with the force of an idea whose time had arrived, the system and its eventual designers found broader inspirations — the German Autobahn, as well as the parkways built by New Yorker Robert Moses as early as the 1930s and the futuristic highway visions of Norman Bel Geddes and French Modernist Le Corbusier.

In a fuller sense, however, it was America's 1950s economic boom that proved the Interstates' true progenitor. The Federal-Aid Highway Act, passed by Congress and signed into law by Eisenhower on June 29,1956, allocated $25 billion to pay 90% of the costs of a 41,000-mile "National System of Interstate and Defense Highways," to be completed by 1972.