I don't think they know we are waiting for them. Unless they know we can eavesdrop on them (and in that case they would never have communicated about this attack in the first place), they are still thinking they will march unopposed at the cities in the delta. That's the whole plan - destroy the delta and starve Astarth. I don't think they know much about us - we have been very good at exterminating their infiltrators in Egypt. Probably all they know is that Astarth employes somebody very good at sniffing them out.
I think their battle plan will be simple - show up in force and try to storm the city with superior numbers (for all they know there is still only the skeleton crew guarding it). Only when that fails will they try something else. Their reliance on Gieloth infiltrators is their weakness here - there are none left alive to tell them we are ready for them.
I've flopped to 3C, this is right on.
Tigranes, I think this is what they know: a powerful immortal arrived in Egypt and took out Sekhenun without warning, then proceeded to take Memphis. Their spies in Thebes recognized that a hunting dog was responsible for the attack, so they notified their more powerful Babylonian allies for reinforcements so that they could retake Egypt. Realizing the threat that this particular immortal posed, they decided to send an extremely large force of men led by probably more than 1 mature Gieloth in order to occupy and reestablish control over Egypt.
What they don't know about is our presence here, because they don't realize that we've been tapping into their network for years. They will be overconfident when they get here because they've been doing nothing but winning for the past four years, and because they think that this will be a minor border skirmish followed by an easy march to Memphis where they will starve Astarth's troops. We can also infer that the Gieloth probably lured all of Astarth's men towards Thebes to make entering Egypt as easy as possible.
They aren't expecting a goddamn thing here, and we must take advantage of that.
I get what
Smashing Axe was saying about the traps being only a one-time measure, but I feel that the effectiveness of the traps during that initial attack will be far greater than the effectiveness of the catapults in the long-term. Yes, the catapults will pester and demoralize the enemy over the long-term, but I doubt that they'll do any real damage or hit any significant targets like Gieloth - even if they did, we'd still have to take out the Gieloth leaders on our own. Which is why I'm advocating C: they aren't expecting to face stiff resistance at all on this "neglected border fortress", they are going to be supremely confident of victory and not expecting us. They don't know that we can tap into their communications.
I personally see this thing as kind of similar to the Battle of Blackwater from
A Clash of Kings. The defenders are vastly outgunned by the attackers, so we need to use the advantage of a surprise trap to even the odds and bring as much death and ruin onto the besieging force as much as possible. If they think that there's only a skeleton crew guarding the place (and all the evidence points to the fact that this is the case), then they will certainly rush in without taking stock of the situation carefully. If we play our cards right, we could kill thousands of their men during the initial assault.