Jeanry, you mentioned two things that interest me a great deal. The use of swords by the Roman calvery and medieval blast furnaces. From my research I have learned that Romans did not use Sirrups and thus did not use lances in their charges. Correct me if I am wrong, but I think their main weapon was the Spatha at about 26 inches. I know that Roman use of Calvery was minimal, especialy early on. I am wondering about the strength of the the Spatha and how it held up in calvery charges prior to the Medieval and Renaisance advances in metalurgy and the invention of the blast furnace. How much weaker was the Roman Spatha or how much stronger were Medieval Swords used in calvery charges. Mind everyone am not saying that I know. I am asking a question.
I was really speaking of Roman infantry, as in the period before the dawn of the Medieval, say arguably the battle of Hastings at 1066 AD, infantry was arguably the strongest fighting arm of the land, for precisely the reason you mention of the difficulties with the saddle and other issues of horse kit.
These collectively seemed to prevent the use of heavy cavalry through most of the Classical era, with a few notable anomolies such as the famous Companions of Alexander of Macedon.
That said, the Romans did have cavalry, often mercenary ("auxiliary" in Roman parlance) and made use of heavy cavalry in the late Imperial period especially (200-450 AD). They did also fight from horseback with swords.
This is a subject of a lot of argument still, but the Romans got the stirrup and high saddle, and thus heavy Cavalry, from either the Goths (who used heavy cavalry successfully against Rome at the battle of Adrianople in 378 AD where Emperor Valens was killed) or the Sarmatians, or some combination of the two, or from the (Persian) Sassanids or from the Huns, depending on who you believe. But either way around the end of the 3rd century AD they were employing heavily armored heavily armed shock cavalry capable of fighting hand to hand.
Bit of background, first thing to keep in mind is that when you are speaking of Rome, it pays to be specific since the Western Roman State alone persisted for over 1000 years, depending on when you date the fall.
The Romans had Iron, probably from the Celts, by the late Republic period, and began producing increasingly "steely iron" by the Mid - Imperial (C. 150 AD). Up to this point their primary 'sidearm' was the Gladius, a medium-short (30" or so) cut-thrust sword developed from the Gladius Hispaniensis adopted from Celts in Iberia (Spain) in Republican times. It gradually evolved from an elegant wasp waisted form into the utliliatrian strait edged, triangular pointed type found at Pompeii from the 1st century AD. The Gladius kept being used until at least the 3rd century, Roman historians insisting that it was vastly superior to the larger Celtic type sword (also used by Germans and other European barbarians) but it was interestingly enough Roman cavalry which started adopting a very similar weapon which we are now calling the Spatha. This was in the neighborhood of 34-36", and like the Celtic weapon similar to an Arming sword except without a heavy iron pommel to counter balance it and without a prominent cross-guard to protect the hand.
It's heavily argued whether the Roman forms influenced the Celtic and later German forms or visa versa.
The Romans did not apparently understand the role of Carbon in their steel, believing the heat treatment was the key, and were obsessed in an Alchemistic kind of way with using different quenching solutions, everything was tried from blood to wine to rose water to beer, to the very Roman minded idea of using the living body of a slave to quench the blade.
It's highly contraversial whether the Celts knew the actual role of carbon or precisely how to introduce it but based on modern tests (and contrary to the claims of contemprary Roman writers) their metalurgy seems to have been better.
All steel production at this time was highly problematic as it had to be laboriously done by piecing together tiny ingots of iron of different qualities usually made from bog deposits. The technique of
pattern welding rose up to make good quality weapons with this bad material (you'll have to look that one up on your own as it's a whole side subject full of contraversy and big with sword collectors)
By the very early Middle Dark Ages crucicble steel began to arrive, allowing much more homogenius (chemically similar) ingots to be made, followed in rapid succession by major advances in water wheel and reduction gear technology which led to a kind of medieval automation of things like trip hammers and bellows needed to get forges hot enough (over 2000 degrees F) to smelt iron. This is when major quantities of good homogenius steel began to become increasingly common all over Europe.
Jr
Edit: PS. All cavalry I know of including Roman cavalry used "lances", in the technical sense of a spear used for thrusting from horseback. The spatha was still a secondary weapon in that sense. The couched use of the lance that you think of from depictions of knights didn't arguably start being used until the 11th century.
The quality of Roman steel could probably be considered inferior to Medieval steel, particularly after the various technical innovations of the 12th century.