Yes - I've seen this. Usually they have a decent defensive position or yours is too strong.

If you probe their lines they will usually (not always) try and catch isolated units which can offer up opportunities.

The worst was a whole network of ditches on the middle east texture with the odd wall thrown in there too.

They are much more obvious on the European map modes.

British hill forts in particular Caractacus' last battle as recounted in Tacitus (possibly Caer Caradog)

BTW - can we make obstacles more obvious in desert terrain - almost lost a battle because couldn't see the edges of an obstacle