Among all these sorts of Masonry, that will always be best which is made of Stones of an indifferent size, rather lesser than greater; to the end that the Mortar penetrating them in more parts may bind them faster, and the strength of the Mortar does not so soon decay. For we see that the Mortar which is laid in the Joints or Seams of the greater Stones with time decays and turns to Dust, which never happens to the most Ancient Fabricks which have been built of little Stones. From thence we may conclude, that it is ill Husbandry to be sparing of Mortar. For this reason _Vitruvius_ proposes another sort of Masonry, which may be call'd the _Compound Masonry_, for it is all the former together, of Stones hewed and unhewed, and fastned together with Cramp-Irons. The Structure is as follows: The _Courses_ being made of hew'd Stone, the middle place which was left void is fill'd up with Mortar and Pebbles thrown in together; after this they bind the Stones of one _Parement_ or _Course_ to those of another with Cramp-Irons fasten'd with melted Lead. This is done to the end, that the abundance of Mortar which is in the middle may furnish and communicate a sufficient Humidity to the Joints of the great Stones which make the _Parements_. See the Figure K. Table I. There are many Precautions to be given to make the Masonry more firm and durable, and these Precautions are common to all the different sorts of Masonry. [Sidenote: _Lib. 1. Chap. 5._] When you would have the Walls very thick, for great and heavy Buildings, you must strengthen the inner part of the Wall with long Piles of singed Olive, which serves for Keys and Braces, for this Wood being so prepar'd never corrupts. [Sidenote: _Lib. 6. Chap. 11._] [Sidenote: _Vide Index._] It is likewise of great Importance for the strength of Walls, that all be directly Perpendicular, and that the _Chains_, the _Pillars_ and _Pieds-droits_ or _Piers_ be so situated, that _solid_ always answer'd to the _solid_; for if there be any part of the Wall or any Pillar that carrys false, it is impossible the Work should continue long. There are also two ways of strengthning the Walls, which are either to ease them of their own weight, or of that of the Earth which they are to support. The first way of easing is in those Places where there are void spaces, as above Doors or Windows. These easements may be made two different ways; the first is to put over the Lintel which supports the Wall, which is over the void space of the Gates and Windows, two Beams, which lying or resting below directly upon _Pieds-droits_ or _Piers_ meet together above.