River crossings

I was defending a river crossing from the enemy Britons as the Julii. There was no bridge, just that sandy ford.

Only thing was that there were two sandy fords (or what looked like two sandy fords. Only one of them was actually crossable, of course, and had I looked closely I would have realised this. However, this being my first battle over a river without a bridge, I just assumed that both places were crossable.

So I split my army in two, and as luck would have it, I place the smaller bunch at the place which was actually crossable.

I only discovered my mistake much later, because the AI, for some strange reason, had lined a huge chunk of its troops up in front of the uncrossable bit of the river as well! I only discovered my mistake when I decideed to push across the river to attack and found I couldn't.

Why didn't the AI just leave a token force to distract the army in the wrong place, and sent the bulk of its troops across the river? They would have destroyed my small force and flanked me! I had 5 onagers, and they would have been easily overwhelmed.

Because the AI is not that smart.

we're talking about RTW here

Off topic, but in MTW there are sometimes 1, sometimes 2 bridges.
Of course one prefers defending 1 over defending 2.
If one places all troops at 1 bridge, the much lauded MTW AI will concentrate all its efforts at that crossing even though both bridges are equally crossable. ~:)

Yeah... it was just pretty strange, because it was a bit like me placing my entire army facing a huge, impassable boulder. The AI would go round the sides to attack, not just sit on the other side.