If you go to the Mies van der Rohe Pavilion, at the foot of Montjuïc, early in the morning, you’ll see it breathing. The porous travertine stone draws in moisture from the air overnight, and as the rising sun begins to heat its surface, the dew evaporates into a mist of water vapour, a long exhale following the slow nocturnal inhalation. The stone, and with it the entire building, becomes a living organism. A great Welsh musician sings that ‘rocks are slow life’; we take that statement not as metaphor, but as a political stance. Stone (and architecture) is a form of slow life, and that viewpoint gives rise to new ways of understanding and exercising our relationship with the built environment, whether through human or natural action—the pigeons don’t differentiate between the cliffside of Montjuïc and a street in the Eixample. The travertine of the pavilion is permeated by life in different ways: it is the sedimentary product of a bio-geological process influenced by water; it replicates the process of its formation through saturation and drying in the short daily cycle made visible by its morning exhalation; and it acts as the support for other types of life that grow and develop in the moisture of its pores—bacteria, algae and moss, key agents in the travertine’s own formation. The stone is simultaneously a product of and a support for life.