Civilization – Ethiopian loyalists won’t give me the land

The shield icon - "Armour" you've called it - is actually a city's combat rating. As with military units¹, the combat rating represents both the offensive and defensive capabilities of city. Therefore, the Walls of Babylon provide +6 to the city's base combat rating.

And yes, this will stack with any other boosts to a city's combat rating. In general, when it comes to stats modifiers in the game, all direct + or - modifiers are applied to the base value first, then all % modifiers are summed and applied as a single multiplier applied (so +20% and +30% is applied as +50%, not a compounded +56%).

_{1. Except for ranged units that have a ranged rating as well - used for attack - while the combat rating for them is defense only.}

Since intrigue is based on what the AI is likely to do, and the AI changes its mind often, it's hard to say if you could be given false intrigue. The false positive rate is nearly impossible to quantify, and from the player's perspective "false intrigue" and "intrigue that changes" are effectively the same.

For instance, let's say AI #1 tells you AI #2 is plotting a sneak attack against you. You build up a military in response, but AI #2 attacks AI #3 instead.

Was AI #1 lying, and the intrigue shared was invalid? Or was your military response sufficient to deflect the attack elsewhere? There's no real way to tell.

I think the practical answer is that you can be given intrigue that never quite pans out. If that's because the AI rethinks, or because the intrigue was a lie is not really possible to determine.

I have never been in a case where I (as the player) could give false intrigue to other civs. I'm inclined to believe that they play by the same rules - all intrigue given to you is true, but subject to change.