How to revert trunk to an earlier revision?

When I look up svn revert it only talks about removing local edits,
but what about this:

Working on trunk and committing a few changes, which later turns out
to be wrong.
Now I want to set trunk head to be at the revision where the edits
started out from.
If I update my wc to that rev I get the state I want but now I cann
not commit anymore...

So how is this done? (I assume it is possible and if done via svn it
should also be reversible).

-- 
Bo Berglund
Developer in Sweden