The most remarkable artwork in Richard Serra’s recent exhibition, which included dense paint stick drawings and sculpture, is Four Rounds: Equal Weight, Unequal Measure (2017). The work consists of four extremely massive solid cylinders of forged steel. Each Round weighs 82.3 tons. One is about waist high; one shoulder high; and the other two are taller but thinner. The experience of walking around or between the components of Four Rounds in the aircraft-hanger scale, visually neutral ground floor Zwirner gallery is easy to describe. What’s harder to explain is why this is a distinctively aesthetic experience—why, that is, that Four Rounds is an artwork. Partly the problem is that it’s hard to cite artistic precedents. Unlike a great deal of contemporary sculpture, this radically abstract Serra has no iconography. And it isn’t about our consumer economy. Once sculpture was taken off the pedestal, it was possible that artworks be confused with mere banal physical things in the world. But Four Rounds isn’t like anything you find in the streets—it is a very singular object. Nor, I should add, does it have any real connection with contemporary architecture.