Maintaining Session Problem - Struts and Tomcat

My Struts application (running on Tomcat 5.5.9) does appear to be maintaining the user's session.  I first noticed that information put into the session was not available after the next call to another Struts Action Servlet.  Looking into it more I found that after each Struts action is performed a new JSESSIONID is created (this was confirmed both by adding logging to the Action classes and inspecting the cookies).  Is there a setting I am missing in Tomcat?

From the web.xml file:
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>

From one of my Action classes:
<code>
public class CitySearchAction extends Action {
    private static Logger log = Logger.getLogger(CitySearchAction .class);
   
    public ActionForward execute(ActionMapping mapping, ActionForm form,
            HttpServletRequest request, HttpServletResponse response) {
       
        ActionMessages messages = new ActionMessages();
        ActionForward forward = new ActionForward();
       
        try {
            log.info("CitySearchAction: Starting...");
            HttpSession session = request.getSession();
            log.info("session = " + session.getId());
...
</code>