It took Neolithic builders nearly 1,500 years to complete Stonehenge, the outdoor enclosure of nearly 100 enormous upright stones on Salisbury Plain in the south of England. The origin of the structure, which is thought to have been a burial ground or perhaps a place of pilgrimage — the stones are aligned to frame sunrise during summer solstice and sunset during winter solstice — defies logic: The iconic 30-foot-tall three-piece sandstone pillars that stand in the center can be traced to local quarries, but how did a civilization without the wheel transport the inner ring of bluestones, some weighing four tons, from their origin point 200 miles away in Wales? Thought to have been finished around 1600 B.C., over the eons Stonehenge has been attributed to the ancient Celtic high priests called druids and the Arthurian wizard Merlin. But modern historians and archaeologists largely agree that a series of indigenous British tribes worked on the site in stages, over hundreds of years, each culture gaining technological sophistication through the centuries, creating an open-air chamber that stands as an indelible template for enclosure, space and ambitious monumentality.

Tom Delavan: My colleague Kurt and I were discussing what qualifies as a room, and we thought, “Well, a room has walls, or something that could define a wall. But does it need to have a ceiling?”

Simon Watson: For me, a room is a place for people to inhabit together in solidarity, I suppose.

TD: So residential, you’re saying?

SW: Not necessarily. It’s a place where people can gather; it’s what we humans do. I tried to go back as far as I could, and Stonehenge seemed like an obvious choice. I’m not sure if we know much about it, but what we do know is that it was a space where people gathered: Whether they prayed or whether they had conversations about their day, it was a place where people came together. And, for me, that was the definition of a room. It doesn’t have a ceiling. And I don’t think the difference stands in the make of walls, but it creates a space.

Gabriel Hendifar: Or is it just about some spatial organization that communicates intention, whether that intention has a ceiling or not? A room is something that’s been organized to serve some function, whether that is spiritual or shelter, residential or commercial.

SW: And you can go forward in history from Stonehenge to the Pantheon, which is one of the greatest rooms in the world. I’m not suggesting that the Pantheon came from Stonehenge, but rather that the circle is a humanist form we understand. It is the shape that creates a togetherness, in a way. It’s instinctual.

Toshiko Mori: Well, also, Stonehenge has a reference to astronomy. It’s human enclosure, with references to the world outside earth. So, the ceiling in this case is a sky. I think that’s the beauty with it, that it actually exists between ground and sky.