Example that wants just what was done in revision 2723 in trunk:
svn merge -c [good_revision] [repository_url]
svn merge -c 2723 http://halsvn01/svn/hal/trunk
This will rollback revision 2723 in trunk, pay attention to the negative sign in front of the revision number:
svn merge -c -[bad_revision] [repository_url]
svn merge -c -2723 http://halsvn01/svn/hal/trunk
Older methods as show by Guillaume below, the one above are now supported and recommended by me.
svn merge ~/branches/features/your-feature-t0-merge-no-ending-slash -r 995:999
Where 995 represent the first revision and 999 represents the last revision to merge
$ svn merge -c 614 https://secreturl/trunk or $ svn merge -r 613:614 https://secreturl/trunk.
The first means apply changes in revision 614 only, while the second form means take all changes required to go from r613 to r614 and apply them here.