Numenorean Defensive Works
Numenorean architecture was massive. Tolkien states that in the fashion of Egyptians, Numenoreans built very large things. This is shown almost immediately upon the Fellowship arriving to old borders of Gondor: Argonath, two massive statues of kings on Anduin, and the Helm’s Gate – a massive fortress said to have been built with hands of the giants. Argonath was built by Minalcar in the 13th century of the Third Age, and that was likely the last such undertaking.
Numenorean architecture however is less Egyptian and more Roman in its nature. Its greatest examples are not religious, but rather imperial. The only time when religious architecture was prominent in Numenor was during the rule of Sauron, a fallen angel: it was then that the big Temple was built in Numenor (whose description makes it a lot like Roman Pantheon, but larger), and many pyramids in Aztec style in Middle Earth, where human sacrifices were performed.
But in all other periods of time, Numenorean architecture is primarily military in nature. We have many examples: Pelargir and Umbar are both large ports, used as shelters for the massive fleets of Numenor. Osgilliath is a port and an administrative centre, while Minas Tirith and Minas Ithil both started out as fortress cities protecting the capital. And in Calenadhorn (Rohan), both major examples of Numenorean architecture are military in nature: Orthanc, a great tower watching the Gap of Rohan, and the fortress at Aglarond.
Situation is no different in Arnor. Lond Daer, the Great Middle Port, is also a military port. Fornost Erain was the “Norbury of the Kings”, a great fortress, and the crossing over Gwathlo at Tharbad was guarded by two fortresses. Annuminas, much like Osgilliath, is an administrative centre and the sole major architectural work that is not military in nature.
Orthanc, Minas Ithil and Minas Anor were all carved from the mountainside – and if Orthanc is anything to go by, reinforced by magic or some skill. The rest appear to have been built in a more classical fashion. Aside from fortifications, Numenoreans also built massive border walls. The Rammas Echor of Pelennor fields evokes the Long Wall of Thrace, a Wall of Anastasius which protected the countryside of Constantinople. In Arnor, there still exist remnants of a massive fortification north of Barro Downs.
First fortresses were built to defend against Gwaithuirim raids, but the major fortifications started being built around the year 1800., a century after the War of the Elves and Sauron. Trade routes and important resources had to be protected, but there Numenor had one advantage: Sauron in the Second Age had no navy, and Numenorean dominance was such that he will not have been able to develop a navy in any case. Numenorean navy easily raided the coasts – but they themselves required local ports of their own. Numenorean fortresses and cities would thus be located at coasts and river crossings, enabling reinforcements to be brought in quickly, while Sauron would dominate the inland, occupying hills and mountains and relying on inland roads.
But since Sauron controlled most of the Middle Earth, he still had the advantage. Numenor could hold the coasts, but could not deploy armies far inland. Any permanent Numenorean colony would have to be heavily fortified, largely self-sufficient, and able to be resupplied by sea. This is how appeared the practice of carving up the mountains. Massive, practically indestructible walls would survive a siege until a relief force arrived. This allowed Numenoreans to take ground step by step – very slowly, but almost unstoppably.
Sauron tried to stop this, and so rivers became battlegrounds. If he could overrun a Numenorean position before fortifications were finished, he could stop Numenorean expansion. Thus rivers were the keys: Numenoreans relied on them when bringing supplies further inland, and Sauron’s armies had to cross them in their movements. Worst fighting was likely in the south, where the Elves could not help Numenoreans, and so Faithful settled to the north.
Massive fortifications make strategic sense in another way also. Numenoreans never grew quickly – their long life meant that they married late, and had few children. There was no need for fortifications in Numenor itself, but in Middle Earth they had to multiply their advantages to make up for the lack of numbers. And these advantages came down primarily to architecture and material sciences: in this one might seek the answer to Numenorean focus on heavy infantry and massive fortifications, both of which maximize these two advantages.
But Gondor, at first, had no need for fortifications. Sauron’s empire was gone, and Gondor’s expansion overland brought it to control large but sparsely populated areas far away from its core. Any threat was minor, and even early Easterling attacks were probably not seen as a major threat. But once tide had turned against Gondor and enemies started conquering its outlying areas, Gondor had no fortifications to fall back on. It also never established a naval supremacy. Thus Umbar had to be destroyed, and by that time the Great Plague had weakened Gondor while Sauron grew stronger. This forced Gondor to retreat, and since there were no physical anchor points in forms of fortresses, it was forced back to the old Numenorean fortresses and the river of Anduin. Nor was there a possibility to build fortresses: the enemy was too strong, and Gondor’s resources too limited. So Gondor continued to rely on old fortresses built during the height of Numenor, or during the initial entrenchment of Gondor. But these were located in the heartland of Gondor, and so by the end of the Third Age the heartland was all that remained of Gondor.
And because Gondor itself was located in Middle Earth, it lost the ability to capitalize on the naval access even when it did have it. In order to expand or survive, it had to protect its population – but plague could not be stopped, and protection from physical threats meant new fortresses, which were never built in sufficient number.