Oh yes you can if you change some files in the game
Ah, cool. I've always wanted to play as Spain or Scythia.
Hmm, I wonder if you can play as the Rebels?
I've just spent some time playing as Carthage, and I have some tactical analysis of their units and general position in the game.
Main points to remember about the Carthagians:
1. Town Militia suck. Seriously, they're not your standard infantry unit, they're for making up numbers and defence ONLY. Iberian infantry are your standard infantry unit.
2. It's quite easy to get a large navy, Carthage, Thapsus and the Sicilian cities are all perfect port cities. It's quite easy to get Triremes quickly too. I, personally, was at war with all four Roman factions [including SPQR] and, to be honest, I owned their navies with ease. I'm not that far in and I could easily blockade all their ports, that's right
ALL OF THEM. That said, the Romans have barely expanded at all yet. They have 7 ports between them, compared to my 5 [hey, since I'm one faction and they're four, that's pretty good]. The Romans also have a strange tendency to transport a large amount of troops across the sea on a whole 1 boat, morons, if their ship sinks, their army is destroyed. I once saw the Scipii trying to move quite a large army complete with THREE FAMILY MEMBERS on one boat that wasn't up to full strength.
3. Also quite easy to get cavalry, they're not the best cavalry in the world, but they suit their purpose well and are quite cheap. I had, after a shortish time playing as Carthage, three or four cities that could produce Round Sheild Cavalry, and Carthage itself could make Long Sheild Cavalry and Elephants.
4. If you're going to play as Carthage, do your very best to take over Sicily ASAP. You can easily move your army in to take the Greek city, then regroup and take the Scipii city. If you wait for the Scipii to besiege the Greek city, then there'll be a Greek army outside of the city near your Sicilian city's border. Your army will crush it easily. When the Scipii see you coming, they'll probably retreat back to their own city, leaving the Greek city ripe for the taking. Once you've got the Greek city, then go for the Scipii one. The Scipii city is the best city on Sicily, and it'll probably have stables straight away, so it'll greatly add to your on-land military force.
5. The Romans want Caralis. They want it now and they will do anything to get it. Anything. Seriously. Building 4 town militia and putting a family member in the city won't do smack, they'll just keep coming. I advise using Carthage and Thapsus to build up a decent army [2-4 Iberian infantry, 2-4 RS Cavalry, more if possible] and puting one of your stronger family members on the island. That'll easily defeat their first few attacks [note: the Scipii and Julii may collaberate and both come at you at the same time]. I advise taking your family member outside of the city every couple of turns to check for mercenaries on the island, there's usually some hoplites and peltasts sitting around near Caralis, recruit them, the hoplites will be a great help. After a few goes the Romans might try landing a big force on the island. I advise keeping a decently sized force in Carthage near a small navy which can quickly rush to land troops on the island and destroy the Roman navy. Working up two decently sized navies and then blockading the Julii and Scipii ports on the west side of italy will also stop them from making more boats without having to defeat your navies first.
6. "Money is the root of all evil," if that's true, Carthage is Satan himself, provided you put up taxes to 'very high' or 'high' in most cities, you'll be raking in 10-20k per turn in no time. After things start getting more expensive this will go down, but by then you'll be well on your way to taking over the world.
Okay, so all of that was quite long, but it's still all true.
Now if you'll excuse me, I need to take over Numidia, Gaul and the Roman factions.