molehills by the yellow Tiber. As the whole city lay on the top of the hill, the space taken in by the walls is necessarily greater than in those towns where the hill stands distinct, the _arx_ alone crowns the top, and where the town walls are placed lower down. The nature of the construction adapts itself to the needs of the different parts of the circuit. The mass of the wall is of polygonal stones, rude, but far less rude than the rudest at Cori. Without being actually laid in regular order, they have a certain tendency to fall into courses as it were of themselves, and it is not always easy to tell how far the roughness of the stone has been from the beginning, and how far it is due to the action of the weather on stones cut perhaps somewhat less carefully than the finer stones at Cori. But the Norban builders could, when it was worth their while, do something more than this. They could, when they had to make a corner, put together squared stones cut with a good deal of exactness, and when it was convenient that a corner should be rounded off, they could do that too with equal skill. This last was done at the greatest gateway looking towards Norma. Here there is no sign of either lintel, arch, or attempt at arch, to span the opening; it would almost seem that the gate itself was simply placed across the opening with nothing over it, much as at Tusculum the gate was hung between two pieces of native rock. That the arch was not known to the first builders of Norba, but that they had reached the stage in which men began as it were to stretch forth their hands towards that great invention, is shown by a ruined building--one of the few things within the wall of Norba which can be called even a ruined building--a little way beyond the _arx_. Here we have a distinct attempt at a vault for the roof; but it is not the apparent cupola of Mykênê and New Grange, nor the apparent barrel-vault of Tusculum. The building is oblong, and the attempted arches rise on both sides, from the small ones as well as from the longer. The ruined state of the building, whatever it was, most unluckily hinders us from seeing how the four vaults, so to call them, were made to meet in the middle. It must have been a strange problem in construction. Hard by is the other building at which we have already hinted as being of later date. It has real arches and masonry, like that which at Cori is attributed to Sulla's time. But it may as well come before the overthrow of Norba in his day as after it.