Explorers

[Magnus]

I was bored one day and ecided to build the unit nobody builds - the explorer. Generally the entire map is already revealed by the time they are built, so what is their purpose?

I will tell you.

Reconaissance.

They move 6! over any terrain and nobody notices them - I have never yet seen any other civ ask them to move out of their territory even when they are sitting right next to a city! Park them on a few choice mountains in the areas of the world that you would like to keep a watchful eye and your knowledge of the enemy will be vastly improved - they are like a distant early warning system of troop movements and such. Use them as cheap spies and you will not be disappointed.

 

[Anglophile]

I agree with you entirely on this use and if one plays on really large maps, one will generally get Explorers well before the whole map is revealed so they can also be used in what I imagine was their designed role.

 

[War4War]

the problem with that unit is that railroads are downgraded to roads as far as they are concerned. So they move slowly on your territory but it's a small problem since they are usually used to explore...i.e. not on your territory.
Also I have been asked by some civs to remove units from their territory and the only one I could find was my explorer. Civs don't complain about trespassing when they don't want to go to war, so it's possible that in your case you were so powerful that other civs didn't mind the trespassing of your explorers.