* @param routes The new list of <code>TradeRoute</code>s.
     * @return An <code>Element</code> encapsulating this action.
     */
    public Element setTradeRoutes(ServerPlayer serverPlayer,
                                  List<TradeRoute> routes) {
        serverPlayer.setTradeRoutes(routes);
        // Have to update the whole player alas.
        return new ChangeSet().add(See.only(serverPlayer), serverPlayer)
            .build(serverPlayer);
    }