It was faced with substantial masonry on both sides, the intermediate space being likewise filled in with stone.

When it crossed bays or morasses, piles were driven to serve as a foundation.

Of course, such a wall as this, by itself, would be no defense.

It was to be garrisoned by soldiers, being intended, in fact, only as a means to enable a smaller number of troops than would otherwise be necessary to guard the line.

For these soldiers there were built great fortresses at intervals along the wall, wherever a situation was found favorable for such structures.
These were called _stations_.