The bulk, if not all, of Gondor's cavalry in this battle consisted of horsemen from the Vales of Anduin (almost certainly men of the Eotheod).

: At the time of the War of the Ring, the cavalry of Gondor are
: mentioned counter-charging the enemy at the Battle of the
: Pelennor Field. This charge was led by the Knights of Dol
: Amroth though the force as a whole was mostly composed of
: horsemen who would seem to have been part of the standing army
: of Gondor.

: The forces led by Imrahil seem to be wholly cavalry (he had a
: long way to travel to Minas Tirith and it would make sense that
: he took only his most mobile troops with him). Imrahil had an
: unknown number of Swan-Knights (probably around 300) and 700
: men-at-arms...

I think 300 is too high for the knights, and the men-at-arms are never said to ride into battle.

: The term Man-at-arms is a very specific one, which Tolkien as
: a Mediaeval scholar would have been aware of, it means a fully
: armed cavalryman whose main weapon was the lance (in French
: Gendarme [from which the modern French term for police comes
: from], though as late as Napoleon's time the earlier meaning
: was occasionally used - a heavy cavalry unit in the Imperial
: Guard was called the Gendarmerie d'Elite)...

Tut, tut! Tolkien was a linguistic scholar. He never called himself a medieval scholar. Someone recently contacted Tom Shippey and asked him what he thought of the idea of Tolkien as a medieval scholar. Shippey's answer (I'm summarizing) was that, if pressed, Tolkien might have conceded to being a medievalist, but not in the sense most people use the word today. But Shippey was quick to point out that Tolkien thought of himself as a philologist, and often said so.

That is really a small nit, but I don't think it's necessary to imply that Tolkien was a medievalist for this point, Martin. I don't know the etymology of "man-at-arms", but Tolkien's philological background would have acquainted him with it.

Nonetheless, he did not feel constrained to abide by the rules, and when Tolkien described the men of Dol Amroth as they marched into the city only the knights are said to be riding horses. The men-at-arms followed, seven hundred strong, "tall as lords, grey-eyed, dark-haired, singing as they came."

As an aside, it may be significant that the swan-knights' horses were grey (like the Rangers of Eriador's horses). Also, I don't know if anyone has ever commented on the applicability of the image of the swan to the knights. These may all have been men descended from Galador. The swan was an image favored by the Teleri in both Aman and Middle-earth (Cf. Galadriel's boat in Lorien).

That is not an argument for or against the men-at-arms being mounted, btw.

:...The man-at-arms could be of any social rank the only
: qualification was the possession of complete armour and a large
: war-horse, this tends to support the distinction of the Swan
: Knights as a social, rather than merely military, elite.

This, I think, is a good reason why the swan-knights may have been men of special descent, but it's only a speculation.

: Tolkien mentions that the inhabitants of Minas Tirith were
: unused to the sight of horses in their city. This should not
: be taken as proof that Gondorians were ignorant of horsemanship
: or did not make use of cavalry to any great extent. A cursory
: look at Minas Tirith, a city built on a conical hill with a
: series of terraces with winding streets, shows what an
: unsuitable place for horses it was. No doubt stabling existed
: beyond the city walls in Pelennor, and even the nobility would
: be forced to take to foot once inside the city proper.

Agreed. In fact, there is reference to stables at the forts for the beacon towers in Anorien.
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