The round towers, however, were not the sole defences of the gates. Outside each one of them was a kind of fence of pointed beams after the manner of a chevaux-de-frise, whilst outside the ditch and close to the bridge stood a barrier, by the side of which was a guard-house. Though 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. The entrance and exit of the Pegnitz were two weak spots, calling equally with the gates for special measures of defence. They were completely barred by "Schossgatter" as they were termed--strong oak piles covered with iron--set beneath the arches that spanned the river. Strong iron chains were stretched in front of them, forming a boom to prevent the approach of boats. The tower at the exit of the Pegnitz was erected, we know, in 1422. It is mentioned by sixteenth-century chroniclers as the Schlayerturm, and, though it has lost its former height, it serves to-day in conjunction with the adjoining building over the water as a jail. The most vulnerable points were thus provided for. The rest of the enceinte consisted of the ditch and walls and towers. There were two lines of walls and towers enclosing a space which in peace-time served as a game-park. Celtes in his poem in praise of Nuremberg boasts of the rich turf growing there, upon which grazed splendid herds of deer. The Tiergärtner Thor, however, did not derive its name from this game-park (Tiergärten), but from another earlier one belonging to the Burggrafs.