Why are some cities limited?

[katank]

They should have hybrid stone/wood walls like the Gauls had though those should be lower and easier to assault than full blown stone walls.

I want them to get paved roads though as movement speed is often a pain.

[Simetrical]

I dont think the barbarians should get to build much more than they do. For starters there just werent that many of them and most of them were nomadic anyway.

There were vast numbers of barbarians, few of whom were strictly nomadic.

In fact all the barbarians should get tougher city defences . . .

Not the Scythians. They were nomadic.

I want them to get paved roads though as movement speed is often a pain.

Nobody of the period except the Romans built a systematic, large-scale paved-road system, from what I understand. This is reflected in the Romans getting highways.

-Simetrical

[katank]

Romans get highways but you'd think that barbarians were able to pave roads too, at least after they conquered some neighbors.

Moving troops through the hinderlands with only a road is extremely painful. In contrast, the Romans not only have highways but are in the tightly packed Italian penisula. This results in traveling the length of Italy in about 2 turns while it takes at least 6 to go through Gaul.

The point if well taken about Scythians as they are far from pseudo civilized Gauls (settled). Nomadic barbarians shouldn't access more disciplined units but should get a extermination/pillaging bonus like the vikings in VI