frontage of a consular army

[Justin Swanton]

Ah ha - I've now been arguing this for some time now.....for Polybius specifically does not say there are 1,200 Velites - I am strongly of the interpretation that there are 1,000 of them - and this means there are exactly 1/3 the numbers of Light Infantry as Heavy.  They form, most likely, the 7th & 8th members of each contubernium.  And, of course, I'll still be plumping for 500ft per legion.

Absolutely right. Funny - I've been studying this for years and I missed the obvious. Polybius clearly talks about a legion numbering 4,000 men - "if the whole number of the legion is more than four thousand..." Livy mentions 4,000-man legions twice. 1,000 velites works fine for the arrangement I described: 400 velites add 2 ranks to the hastati, 400 add 2 to the principes, and 200 add one rank to the triarii.

Not sure about them being part of the contubernium. That was a later unit of the Marian and post-Marian legion. Hyginus describes it in the context of a first-century camp.

And 500 feet = 167 yards, which is 33 yards short of my 200 yards and hence 83.5%. A pass mark. I won't fight about it. ;-)

But what I am indeed surprised about is how you think they are equipped for melee combat - for with: no armour; a small shield probably only used to catch incoming missiles; and possibly just a dagger, they certainly don't seem to be.  I suggest it's much more likely that, after their skirmishing role is over they are most probably employed finishing off the wounded enemy that have been walked over and/or dealing with the wounded and removing them from the battle line.

μάχαιρα is a flexible term. It can mean a large knife or a small sword. It can certainly be used for hand-to-hand combat:

But if it is necessary to make a military expedition anywhere, those who have been thus educated take the field, no longer with bow and arrows, nor yet with spears, but with what are termed “weapons for close conflict” [ἀγχέμαχα ὅπλα]—a corselet about their breast, a round shield upon their left arm (such as Persians are represented with in art), and in their right hands a sabre [μάχαιρα] or bill. - Xenophon, Cyropaedia: 1.2.30

The πάρμη is a light shield, true, but the velites didn't need a shield to protect themselves from enemies' missile fire. The leves were not equipped with shields and strict skirmisher class troops like Greek psiloi didn't have them either. You don't actually need a shield to protect yourself from enemy missiles. This video shows how skirmishing could go on for ages between unprotected opponents with very few casualties. The parma is light just as the machaira is small, to allow the velites to be fast and mobile and yet be able to engage in melee combat. I see velites as a rough equivalent to peltasts, able to take on cavalry at a pinch and support heavy infantry, though not in the front ranks.

Which raises the question: how does adding ranks support an infantry line? The rorarii did that but how did it help? My best-fit hypothesis is that it largely acted as a discouragement to enemy infantry who, seeing a thicker line, would feel they could not break it. Too many men to fight through. And if the men in some files were wounded or killed the velites could keep the line intact until the battle was won elsewhere. 

For me though the real clincher is the fact that the velites are part of the hastati, principes and triarii maniples, which implies they work with them, and the best role I can think of is rear rank support.

As for the Marian Legion - are you forgetting the 'lighter troops' (cf Caesar)?

Quote me that? Were these troops an integral part of the legion or were they specialist detachments meant for specific tasks?