I was interested that you many have had a contrary point or some interesting obscure historical factoids to share, but between using "Falcata" and "Dacians" in the same sentance and referring to the Portugese as a "happy fishermen tribe with a funny accent" you lost all credibility as far as I am concerned.

Now here's my whole take on how the Romans managed to conquer the known world and grow as they did, a combination of versaitlity, tactical awareness, diplomatic cunning and a bit of luck.

When I think of the Roman army the first thing that comes to mind is "versatile" the Romans used superior logistics and engineering techniques to take advantage of any situation and hence their infantry developed into a versatile soldier capable of filling many roles, to exemplify this examine their equipmen.

The short stabbing Gladius sword
Chain or banded mail armor depending on the time period
The large Scutum shield
And the Pilum

Generally, the Romans would advance before their enemy, unleash their pilum then charge pushing forward using the force of weight to knock the enemy back while stabbing at whatever was in front of them. However they were fully capable of filling other roles such as using their heavy pilum to form a sort of in-prompt to spear wall as a defence against calvalry, like all heavy infantry they were vulnerable to flanking by calvalry and light infantry but in their zenith at least the Romans were fully aware of this and made efforts to ensure it didnt happen. A lax in taxtical awareness like that mentioned above and a signifigant growth in arrogance and a belief in invicinibility is what lead to them being utterly annihalated by the Goths much later.

The Romans also used their logistical and engineering skill to make sure they were in the most advantageous position possible in battle, and as Aymar stated earlier, that can go a long way in winning a battle.

Also if you look at the way Rome expanded, they knew "exactly" when to strike at a foe, just look at the Gauls. The Gauls were fully capable of fighting and defeating Romans, and they had proved it before...However, when Ceasar expanded into Gaul they were at civil war amongst themselves with the various tribes and their military was really a shadow of it's former power. The Gauls were capable of functioning as an oprganized and very effective military force, but Rome "caught them with their pants down" so to speak.

In effect, what I'm saying is that the entire notion that Rome, or any people are just "better" then another is stupid. There are extenutating circumstances, political/economic landscapes, tactical decisions and realities and yes, even luck that determines who is in power, when, and how. There are pros and cons to every military formation, nothing is an "end all beat all" way of doing things, its all a matter of how the cards are played.