How do you form an alliance in Travian?

You need to:

Build an embassy

Get it to level 3.

Then, go in your embassy and you will get the option.

n.b. Tag is a shortened name for the alliance (the one displayed in stats) and name is the full one (only displayed on the alliance page.

So you could have:

Tag: Eg Name: Example

BUT

Tag: Example Name : Example works.

No 2 tags can be the same per server (unless one deletes/ changes).