Space that’s enclosed is different from space that’s not and, with caves, those spaces are defined by the inner surfaces of the cave and by the cave mouth. The cave mouth is the boundary between inside and outside because it’s the only surface that has an other side. If humans are supposed to have an innate biophilic preference for open savanna landscapes, then we might and with equal justification also have one for cave-like spaces not artificially and obviously defined by those modern inventions we know as load-bearing walls. I’m beginning to think I do. 

Whether humans are innately caveophilic or not, there was never going to be sufficient caves to go around. Their geographical distribution was uneven and their locations inconvenient. Sometime prior to 4000BC walls were invented to simulate the shelter advantages of caves but cave-like spaces continued to have a special hold on mankind. Dating from 4800BC, the Cairn of Barnenez is the oldest building in the world. It’s a series of tomb chambers created by piling and arranging rocks.

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The Great Pyramid of Giza was built 2580-2560BC. Once again, a small mountain of rock was shifted into place, and again as a tomb. Once more, the shapes of the interior spaces have no relationship to the mass from which they are created.

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This is the Temple of Abu Simbel from Egypt circa 1300 BC.

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Badami Cave No. 3 dates from the 6th century and is dedicated to Hindu deity Vishnu. The columns can’t not support the mountain in some sense but it’s possible the ceiling acts as a monolithic transfer beam and the columns are there to structure the ceremony itself. [For how could one calculate their size and spacing? If they were empirically deduced by trial and error then we would expect to see a history of errors.] 

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The geology of parts of northern China permitted people to dig into cliff faces and make artificial caves for living in. These houses are called yaodong. 

There are also sunken yaodong for places not blessed with cliffs. Yaodong are lived in by some 40 million people and out of choice so they are more than some archaic curio. The 2013 post Architecture Without Architects has some more images. 

The spaces inside a sunken yaodong are identical to those of a cliff one, and this central space functions in the same way as would the outside, but is now a new type of space, neither fully-public nor fully-private – it is communal space that links and buffers between the houses and ground level public space. Many of the underground houses in the town of Coober Pedy in South Australia are hybrids of cliff and sunken.   

It is rare to have internal space conceptually as well as physically separated from external space. In 1964 Kazuo Shinohara presented House of Earth (Space in Black) as architecture and within less than a year completed House of Earth [aka House With an Underground Room]. The idea of an architecture comprised of internal space and nothing else is a fascinating one but an architecture that denied the exterior was never going to lead anywhere and Shinohara explored it no more. Tornado shelters and nuclear shelters are examples of spaces physically separated from the outside [and for very good reasons]. Survival has no need for art or architecture.

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I can’t say what this next building is or when or where it’s from but I suspect Neolithic Europe, possibly (what we now know as) Scotland. [Dec.17: I’ve since learned it’s one of the Ġgantija Temples in Malta (c. 3600–2500 BC). Thanks David!] I also suspect it’s later than Cairn of Barnenez [4800BC] because

• Although the spaces inside have no relationship to what we see on the outside, their axial symmetry implies the performance of some ritual or ceremony by the living.
• In addition, the number of spaces suggest more than one activity taking place. 
• The construction is more sophisticated as the greater part of the building mass is infill stabilised by rock “formwork” – a method that requires smaller quantities of premium materials.
• The design is better suited to flat land as it does not depend upon digging into a cliff or making a cliff by excavating a hole.

We’re getting closer to the invention of that spatial separator we know as the load-bearing masonry wall. Even these proto-walls support themselves and at the same time define the boundaries of this new thing called “space”. 

In time, the edge of space would become synonymous with the elements defining it and produce what we know as inside and outside but it’s not as if the planet’s population suddenly discovered the joys of detached houses. Walls still required materials and labour that might be better used for other things and having fewer walls meant sharing them. Whereas the sunken yaodong created an artificial cliff around which the house was built, the courtyard houses of Mesopotamia or Egypt can be thought of as houses built around an artificial hole that didn’t need digging. On three of the other sides of the house were other houses that did the same. Space the other side of the party walls has no meaning other than the side used for access.

The courtyard house permitted occupants adequate daylighting and ventilation and separating them by party walls meant denser settlements requiring less labour and resources for their construction. 

Middle Eastern houses still tend to be gated communities for individual families. 

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The next step in the history of the wall was to inhabit it. Over in Europe, castles had courtyards for similar reasons whether for a single (extended) household or for multiple occupancy. Building castles in inaccessible locations and adding fortifications to them solved problems of security and permitted some openings on the outside. 

Spatially, the infill in the image (on the left) became inhabited space (on the right) with outside space on one side and courtyard space on the other.  

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The idea of habitations forming a wall divided the world quite conveniently but it was not unique to Europe. The circular hakka houses of the Han people in southern China are houses built within a circular wall that originally served a defensive purpose.

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Things improved over the years but it was still better to be on the inside rather than the outside in Florence circa 1450, especially if you were well-off. The outside of this building presents itself as a barrier between “civil society” on the inside and some still very real threats outside. 

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The European courtyard house with its openings on both public and private sides is a refined inhabitable wall that readily upscales (back) to multiple occupation housing with public space on one side and communal on the other. 

One recent example had public space as the edge on one side and privatised (pseudo-public) space as the other edge.

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As an invention, it wasn’t new but it needed rediscovering anyway.

I see now that my own explorations of the past year have been circling around this topic of the edge of space when the spatial divider is an inhabitable wall. It was present in this recent proposal for apartments overlooking a mall atrium in Living Above Shops

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 and also in my proposal for The Uncompleted Apartment.  

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This notion of an inhabitable wall as the edge of space makes sense of some of my favourite things despite their differing scales. In Milan’s Galleria the inhabitable wall is the edge of private space mediating between public and communal public space. In Walden 7 the inhabitable wall is again the edge of private space mediating between public space and communal private space. In Uncompleted House (and others such as Repeating Crevice) the habitable rooms are a wall of private spaces mediating between outside space and shared circulation space. Walden 7 has an imposing external appearance but all three have the primary architectural action on the inside edge of space.    

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This notion of the inhabitable wall as spatial divider has the potential to be a more sustaining way of configuring the buildings we actually use and that have meaning for us in our daily lives. However, it’s not something that’s likely to happen on its own for it makes no sense for today’s architectural branding machines to devise architectural experiences resistant to capturing and propagating as images and visualisations. Regardless, it makes economic sense to confine architectural invention to the intensively used spaces that can’t be done away with, and it makes social sense to have a shared architectural experience reside in spaces shared by all users. 

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