Motional be

In The Cambridge Grammar of the English Language (p.113-4), this is called "motional be", and it's very unusual as English verbs go. In this meaning, be appears only in perfect constructions:

(present perfect)　　We have been to Paris twice.
(past perfect)　　　 By 2008, we had been to Paris twice already.

This is not possible without the perfect:

(present simple)　　＊We are to Paris.　　 ←　ungrammatical
(past simple)　　　 ＊We were to Paris. 　 ←　ungrammatical

The perfect construction have been to X is an experiential perfect. It means you've gone to X in the past and have (probably) since left; now you have the experience of having gone there.