The first of Smithson’s major outdoor earthworks intended to exist exclusively outside, ​Asphalt Rundown​ is a demonstration of what Smithson called the “crystalline structure of time.” He argued that time does not pass so much as it builds upon itself. In a quarry outside of Rome, Smithson poured a truckload of hot asphalt down a steep embankment, which cooled and hardened as it fell. The resulting sculpture can be seen as time frozen, mid-flow, or as yet another sedimentary layer in the infinite accumulation of time.