When common lime answers our purpose, we do not trouble about Roman cement.

Now Eumenes Amedei requires a first-class cement, even better than that of the Chalicodoma of the Walls, for the work, when finished, does not receive the thick covering wherewith the Mason-bee protects her cluster of cells.

And therefore the cupola-builder, as often as she can, uses the highway as her stone-pit.
With the mortar, flints are needed.

These are bits of gravel of an almost unvarying size--that of a peppercorn--but of a shape and kind differing greatly, according to the places worked.

Some are sharp-cornered, with facets determined by chance fractures; some are round, polished by friction under water.