For the time, these works appeared strong, and the axiom in fortifications, "What offers itself as a defence ought to be defended," was already pretty generally adhered to. Fig. 60 gives the northern work which was destined to sweep the plateau, and to render difficult the approach to the cité on this its very accessible side. This work consisted of a ravelin, A, whose height above the level of the plateau was not more than six feet; next of a first tenaille, B, with orillons, eighteen feet above the plateau, and a second tenaille, C, three feet above the level of the tenaille, B. Two bastions, D and F, enveloped the two great towers, G and H, which were terraced. The platforms of the latter rose three feet above the platforms of the bastions. The gate, I, of the fourteenth century, had been preserved and repaired, and the curtains, K, terraced to receive cannon. [Illustration: FIG. 61.] The road passed over the right face of the ravelin, and thence at right angles to the centre of the tenailles. A wide fosse, E, protected the exterior works, and a second fosse, L, the curtain of the second tenaille. Fig. 61 gives a sketch in perspective of the bastion, F.[51] No use, however, was made of these defences till about thirty years after their construction. FOOTNOTES: [Footnote 50: In plan not straight, but broken by a series of returns each in advance of the other.] [Footnote 51: Of the general plan, Fig. 59.] CHAPTER XIV. _THE SIXTH SIEGE._ About the beginning of July, 1636, France, governed by the Cardinal de Richelieu, saw its northern frontier invaded by the too celebrated Jean de Weert, with an army of Hispano-Belgians, to which the empire had added a numerous body of cavalry, composed of Poles, Hungarians, and Croats. These allied troops advanced into Picardy, and Paris was, for the moment, anticipating a siege; but the enemy were delayed by the siege of Corbie, and, having taken this town, in which they left a garrison, they retired for fear of being taken in rear by the Dutch.