Quote Originally Posted by O'ETAIPOS
Train of artilery? Maybe they meant "training of artilery" and then this is not very informative, as torsion machines were also called artillery. On multiple rings of walls - if the last ring is early modern fortification then having older rings inside is perfectly historical.
A train of artillery is an Early Modern Age military term referring to an organized assembly of gun pieces destined to put a fortified position under siege.

About multiple rings of walls, they were usually made on purpose -so that secondary line walls dominated the exterior ones and could help in their defense. When a city built a larger wall around was not usually to add another wall to defence, but to allow city growth, since the old ones were now not large enough to encircle the whole city, and exterior buildings and citizens were without protection. Inner older walls were usually demolished to allow new housing and streets, and because of the construction materials being reused -building walls was a very expensive matter. The existence of another smaller but mightier citadel or military keep inside the town was common, tho. That was usually where the city garrison was quartered.