I am playing an online game (huge, continents nine AI's) with my friend. He sent a great merchant into my continent. I spotted the merchant in the middle of my empire, declared war and killed it. He says I should have never been able to see the merchant unless we were at war. In a previous game I landed a merchant in his empire, then asked him if he could see it. He couldn't. My ability to see his merchant has really surprized him. Needless to say he is po.ed! :p So what gives?

I think the only unit that is invisible is the spy. I suppose the merchant could have been invisible to him if it was outside his cultural borders and he had no units in the vicintiy of the GM.

The submarine is also invisable (for the most part).

The Great Merchant could also just have blended in also though.

The great merchant should be visible to anyone who can see the tile it is standing on. Only spies and subs are invisible.

So what gives?

What gives is that your friend doesn't have a good understanding of Great Merchants. They are not invisible in any way, shape or form. He likely misunderstood the bit about them being able to enter other civ's territory without an Open Borders agreement and thought that meant that they couldn't be seen.

However, when you declared war on him, I thought all of his units that were inside your territory would be moved outside of it automatically. Did that happen and you killed the GM from where he got moved to or did he remain inside your borders? I'm not sure whether the enemy units' moving was due to the declaration or war or the cancelling of the Open Borders, in which case the GM would ignore that and stay where he was.

He likely misunderstood the bit about them being able to enter other civ's territory without an Open Borders agreement

Which units have this property, and where is it documented? By trial and error, I think caravels and spies do and missionaries, scouts, and explorers don't.

However, when you declared war on him, I thought all of his units that were inside your territory would be moved outside of it automatically. Did that happen and you killed the GM from where he got moved to or did he remain inside your borders? I'm not sure whether the enemy units' moving was due to the declaration or war or the cancelling of the Open Borders, in which case the GM would ignore that and stay where he was.

Actually, I am pretty sure that units which can traverse your territory without open borders (i.e. great merchants, caravels etc.) will not be moved out when you declare war.

J.

Well the first time he must not of noticed. Weird though because I also sent over a couple military units to gift as he was at war. He saw the military units but not the merchant. Mabe he didn't look closely enough even though I asked him if he could see a merchant several times and he couldn't. Weird. Anyway, I did see his merchant before I declared war and killed it where it stood after. He couldn't move it as it was my turn. War had no effect on the merchants location within my borders.

Which units have this property, and where is it documented? By trial and error, I think caravels and spies do and missionaries, scouts, and explorers don't.
Submarines can ignore closed borders as well.