5. The bulk of the artillery of the defence should be outside the forts; the direct-fire guns preferably in cupolas, the howitzers in concealed positions. 6. The forts should be connected by lines of entrenched infantry positions and obstacles, permanent bomb-proof shelters being provided for the infantry. 7. There should be ample communications--radial and peripheral--between the place and the forts, both by road and rail. 8. Special lines of communication--such as mountain passes--should be closed by barrier forts. These considerations will now be taken somewhat more in detail, but first it will be useful to deal with the plan of Metz in 1899 (fig. 44). Metz. Here the fortifications of successive periods can be readily recognized. First the old enceinte, unaltered by the Germans and now _declassee_. Next the detached forts, begun by the French engineers in 1868 and still unfinished in 1870, can be readily recognized by their bastioned trace. Among them are Fort Manteuffel, formerly St Julien, and Fort Goeben (fig. 45), formerly Queuleu. These were not altered in their general lines. [Illustration: From Plessix and Legrand's _Manuel complet de la fortification_, by permission. FIG. 45.--Fort Goeben, Metz.] This early line of detached forts, less than 3000 yds. from the enceinte, was completed by the Germans with forts of polygonal type such as Fort Prinz August. The hill of St Quentin (fig. 46), a very important point, was converted into a fortified position, with two forts and connecting parapets, and a communication running north to Fort Alvensleben. The arrangement of wing batteries in connexion with the forts can be clearly noted at Fort Manteuffel. These are reinforced by other batteries either for the defence of the intervals or to dominate important lines of approach such as the valley of the Moselle (canal battery at Montigny). To these were added later armoured batteries. There are also infantry positions, shelters and magazines in connexion with this line. Finally some new forts of modern type were commenced in 1899 at about 9000 yds. from the place. Fortresses. Leaving out of consideration at present the strategic use of groups of fortresses, the places which, as mentioned above, are intrinsically worth being defended as fortresses are:-- (a) Centres of national, industrial or military resources. (b) Places which may serve as _points d'appui_ for manoeuvres. (c) Points of intersection of important railroads. (d) Bridges over considerable rivers. (e) Certain lines of communication across a frontier.