[Aiwendil]

Some interesting speculations about Orthanc. I could imagine what we call a volcanic caldera being, in Middle-earth’s terms, the site of a battle between Melkor and the Valar (in their early wars), or something like that.

But Rumil is right that the works of the Numenorean exiles in their days of glory exhibit some similarities in construction. Even if Minas Anor, Minas Ithil, the Hornburg, the Deeping Wall, etc., were not all literally carved out of solid rock, the appearance of being so may have been an aesthetic goal – one that was accomplished by actually carving the living stone when possible and, when not, by using their skill to fashion the walls very accurately and hide the joints between stones.

In this connection it’s possibly worth mentioning that Tolkien may have been influenced by the Anglo-Saxon phrase ‘enta ge-weorc’, ‘work of giants [ents]’, which seems to have been used to describe ancient Roman buildings that they viewed, to some extent, with awe. Tolkien similarly describes both the Hornburg and Minas Tirith:

There upon its spur stood high walls of ancient stone, and within them was a lofty tower. Men said that in the far-off days of the glory of Gondor the sea-kings had built here this fastness with the hands of giants. The Hornburg it was called . . .

And upon its out-thrust knee was the Guarded City, with its seven walls of stone so strong and old that it seemed to have been not builded but carven by giants out of the bones of the earth.

And Tom Shippey makes an interesting argument for the origin of Orthanc lying in this phrase from the Cotton Gnomes:

orþanc enta ge-weorc

This is usually translated as ‘cunning work of giants’, but Tolkien may have preferred to read ‘orthanc’ as a name rather than an adjective: ‘Orthanc, work of giants’ or even ‘Orthanc, fortress of giants’ (‘ge-weorc’ can generically mean ‘work, building’ but very often means specifically ‘fortress’).

William Cloud Hicklin wrote:

One also wonders if the tunnels where the circles of Minas Tirith passed through the 'keel' were barred by gates and/or potcullises, and whether galleries with loopholes and murder-holes were installed.

This is an interesting question, because as far as I can recall there are no references to arrow-slits or murder-holes in any of the fortifications described – but they’re such a prevalent feature of castles in the real world that I would expect they must have existed in Middle-earth.

Rumil wrote:

There seems to have been some really long wall (like Hadrian's?) around Arthedain, the hobbits cross it after they leave Tom on their way to Bree. Also the chain of forts and watchtowers on the Weather Hills, perhaps adding up to some 'Roman limes'-type system? Probably these would be ordinary stone and mortar, being built long after the decay of Numenorean craft/tech.

I had quite forgotten about that wall. Indeed, it seems to have been part of a whole system of defences on Arthedain’s border. Presumably, like Hadrian’s wall, it was of more use in preventing disorganized bands of raiders from crossing the border than in actually holding back an enemy army. It seems likely, then, to have been built relatively late, when Arnor had begun to become a more lawless and less civilized place.