At the time of the construction of these and the other lofty towers it was still thought that the raising of batteries as much as possible would increase their effect. In practise the plunging fire from platforms at the height of some eighty feet above the level of the parapets of the town wall can hardly have been capable of producing any great effect, more especially if the besieging force succeeded in establishing itself on the crest of the counterscarp of the ditches, since from that point the swell of the bastions masked the towers. But there was another use for these lofty towers. The fact is that the Nuremberg engineers, at the time that they were built, had not yet adopted a complete system of flank-works, and not having as yet applied with all its consequences the axiom that that which defends should itself be defended, they wanted to see and command their external defenses from within the body of the place, as, a century before, the baron could see from the top of his donjon whatever was going on round the walls of his castle, and send up his support to any point of attack. The great round towers of Nuremberg are more properly, in fact, detached keeps than portions of a combined system, rather observatories than effective defenses. The round towers, however, were not the sole defenses of the gates. Outside each one of them was a kind of fence of pointed beams after the manner of a chevaux-de-frise, while outside the ditch and close to the bridge stood a barrier, by the side of which was a guard-house. Tho it was not till 1598 that all the main gates were fitted with drawbridges, the wooden bridges that served before that could doubtless easily be destroyed in cases of emergency. Double-folding doors and portcullises protected the gateways themselves. Once past there, the enemy was far from being in the town, for the road led through extensive advanced works, presenting, as in the case of the Laufer Thor outwork, a regular "place d'armes." Further, the road was so engineered as not to lead in a straight line from the outer main gates to the inner ones, but rather so as to pursue a circuitous course. Thus the enemy in passing through from the one to the other were exposed as long as possible to the shots and projectiles of the defenders, who were stationed all round the walls and towers flanking the advanced tambour. This arrangement may be traced very clearly at the Frauen Thor to-day. The position of the round tower, it will be observed, was an excellent one for commanding the road from the outer to the inner gate.