def create_milestone(self, project_id, title, deadline, party_id, notify):
        """
        Creates a single milestone. To create multiple milestones in a single
        call, see the "create (batch)" function. To make a company responsible
        for the milestone, prefix the company id with a "c".
        """
        path = '/projects/%u/milestones/create' % project_id
        req = ET.Element('request')
        req.append(
            self._create_milestone_elem(title, deadline, party_id, notify))
        return self._request(path, req)