I have recently bought this one, I used to play Caesar 3 when I was little.
I have made a somewhat useful town, with some industry, but I always lose to the barbarians, it doesn't matter if I have the same amount of soldiers or even a little more (The maximum I have was 3-2 in my favor), they keep winning no matter what. Also, how should I increase the amount of soldiers I get?
I have watched two youtube series on the game (gamerZakh and KaioGamer, in spanish) and both seems to lose all the battles too, so, what am I doing wrong here?

Any other tips that are not clear about the game are also welcome, like how to make the industry more eficcient. :D

No, it's about Caesar 1, I have been playing with Augustus mod for Caesar III and is really good! :D

There is this thread for a good start. I also struggle with this game and gave it another try. Building amenities (forum, school, market, temple) and infrastructure (fountain, bath house) followed by houses in the vicinity works (stopped at ~900 population, ~160 denarii population tax). I built 1 heavy industries unit further away and also workshops (first 2x excellent and 1x good) and later more, but only got industry tax for 2 years and then it stopped. Fixed cost per year are at ~240 denarii. Any recommendation how to make a profit and how fast to expand?

I realize this thread is more than one years old, but just in case someone else is wondering later:

As stated in the manual, different barbarian clans react differently to the 4 buttons you have in battle.
Unfortunately, there is no cheat sheet for this, just save before the battle and try which one works. Also note that if you have a lot less men or a lot lower morale then you lose by default. On the same map the same button will work every time. On the next map you will have to figure it out again.
You can increase the number of warriors in the forum. Click the guy in the millitary gear to increase either spending or conscription. Conscription is free but conscripted soldiers are weaker and it will also increase the risk of revolt in your city.
Clicking the lady serving up food takes you to the pleb screen. Every 16 pleb assigned to millitary duty also increase the number of your warriors by 1. Any less and it doesn't do anything. Also be careful when building forts. If you build a fort it will split your warriors into 2 groups, meaning the individual groups will be weaker. My recommendation is having just one cohort and save scumming.

Good luck to anyone still playing this amazing game!