What is the point of the Rammas Echor?

Question

In the Return of the King novel, the men of Gondor build a defensive wall around Minas Tirith, known as the Rammas Echor or Outwall. The area that the wall encloses stretches almost out to Osgiliath, and the construction is relatively new, as mentioned in one of Gandalfs conversations with the Gondorian soldiers on crossing the outwall.

After re-reading ROTK, I keep noticing how bad of an idea building the outwall seems to have been. In no particular order, the flaws of the outwall are:

• It encloses way too big of an area, with a length too long to be defended by the number of troops Gondor has on hand. In the book it is confirmed that the outwall was breached by Mordors forces in multiple places, and at least partially hinted that this was due to the defenders being spread too thin
• The building of the outwall consumes a great deal of manpower and resources for a wall that cant effectively be held
• Given limited manpower in a defensive role, it makes little sense to use it garrisoning walls of ordinary quality when compared to the main walls of Minas Tirith (mentioned to be of unbreakable quality of almost a supernatural nature due to their age/craftmanship)
• Once the outwall is overrun, it provides a ready made defence against any reinforcing armies that might arrive to try and relieve a siege of Minas Tirith (Rohirrim or otherwise).
• Most importantly of all, if overrun and manned by Mordor, the outwalls northern side acts as the most impassable obstacle possible for the Rohirrims entirely mounted armies (which Theoden mentions was only avoided by blind luck that the Orcs manning the Northern wall began to destroy it). Literally the only workable play in Gondors playbook counts on help coming from Rohan, but the building of the outwall runs the risk of ruining that plan even if everything went right

Basically it seems to me that building the outwall is a bad idea. If you cant defend the outwall (and all signs say they cant), you'll end up defending the city walls in a more hopeless situation than before, so you might as well have not built it in the first place.

Answer 1

Gandalf's comment to Ingold as he and Pippin pass through the wall is (emphasis mine):

And as for counsel, to you I would say that you are over-late in repairing the wall of the Pelennor.

This is a long-standing wall, that had fallen into disrepair over the centuries. They're simply repairing and reinforcing it, not building it from scratch.

Answer 2

Historically, an outer wall will deter raiding

An outer wall enclosing a larger area is not unprecedented in world history. Perhaps the best example would be the South Indian city of Vijayanagara. This city was capital of an eponymous empire from around 1400 to 1560.

The city had multiple rings of fortifications; a Persian traveler (Abd-al Razzaq) in ~1440 says seven. The innermost areas were crowded with temples and marketplaces. Much of this area survives today in ruins as the UNESCO World Heritage site of Hampi. The outermost wall was reported to be 60 miles in circumference, by an Italian visitor (Niccolo di Conti) in ~1420. This could be extrapolated out to an estimated area of around 600 km$^2$, since the walls are less than perfectly circular. According to A Short History of India, the outer areas were "occupied by fields and gardens watered by canals from the river" (quote sourced through Wikipedia). Estimates vary for total population, but 500,000 within the outermost walls, with most of them concentrated in the central city, are reasonable (Chandler estimates between 400,000 and 600,000 during the height of the empire).

So, such outer walls as described by Tolkien did exist on Earth. But the question is "what is the point?" Well, a particular problem faced by the Vijayanagara Empire were raids from the Sultanates in the northern Deccan, such as the Bahmani Sultanate and its successors. An outer wall isn't easy to defend and as such won't stop an invasion in force, such as orcs backed by siege trolls. On the other hand, a wall is excellent at stopping raiders on horseback. If you have a continuous stone wall that is at least 10 feet high, there isn't really a good way for a few dozen horsemen to cross that in hopes of pillaging or capturing some slaves. This is the same principle behind the construction and nearly two millennia of maintenance to support the world's most famous wall.

Conclusion

Outer walls, high but undefended, are an expensive undertaking, but make a lot of sense if their purpose is not to withstand siege but to deter raids. They were used on Earth and they probably worked well enough to keep the various worg-riders of Moria at bay. You can't feed all of Minas Tirith from the relatively small area enclosed, but you can keep most of your animals and valuables inside of it, and grow most of your vegetables and fruit, while collecting staple grains and fodder from a wider area inside.

Answer 3

There have been some excellent points (which I upvoted) made about the wall merely being repaired and not being newly built, and also that keeping troops busy is essential to maintaining morale, and they are doubtless the main reasons for the work being done on the Pellenor walls.

I'd like to add one more tactical value that wall brings: It focuses the enemy advance. Even a modest wall needs to be knocked down for an enemy force to advance across it, and even then it remains as a line of rubble which must be crossed. The tendency is for the advancing forces to penetrate the wall (probably in many places) and for the force to enter through those breaches. This is ideal from a defender's point of view, since, for a time, only a fraction of an otherwise overwhelming force can be brought to bear.

This won't stop the enemy, but it is effort expended before battle (when soldiers' time is cheap) which multiplies their effectiveness when the onslaught arrives. It won't guarantee victory (what does?) and in this case didn't help much. But since planning must be done before the enemy's forces and plans are known, it's a very sensible precaution, provided it's done late in the game. (It's more important to make sure Minas Tirith's walls are solid and the defences at the Anduin, for instance, but once things like that are done, it's a very sensible precaution.)

Success in war is based on getting your opponent to do what you want...and being prepared when your opponent does something you didn't expect. In war, there's a term for people who devise a perfect strategy and focus on it: Losers.