164. And this example from Lucca is of a very important class indeed. It is from above the east entrance gate of Lucca, which bears the cross above it, as the doors of a Christian city should. Such a city is, or ought to be, a place of peace, as much as any monastery. This custom of placing the cross above the gate is Byzantine-Christian; and here are parallel instances of its treatment from Assisi. The lamb with the cross is given in the more elaborate arch of Verona. 165. But farther. The mosaic of this cross is so exquisitely fitted that no injury has been received by it to this day from wind or weather. And the horizontal dressed stones are laid so daintily that not an edge of them has stirred; and, both to draw your attention to their beautiful fitting, and as a substitute for cement, the architect cuts his uppermost block so as to dovetail into the course below. Dovetail, I say deliberately. This is stone carpentry, in which the carpenter despises glue. I don't say he won't use glue, and glue of the best, but he feels it to be a nasty thing, and that it spoils his wood or marble. None, at least, he determines shall be seen outside, and his laying of stones shall be so solid and so adjusted that, take all the cement away, his wall shall yet stand. Stonehenge, the Parthenon, the walls of the Kings, this gate of Lucca, this window of Orvieto, and this tomb at Verona, are all built on the Cyclopean principle. They will stand without cement, and no cement shall be seen outside. Mr. Burgess and I actually tried the experiment on this tomb. Mr. Burgess modelled every stone of it in clay, put them together, and it stood. 166. Now there are two most notable characteristics about this Cyclopean architecture to which I beg your close attention. The first: that as the laying of stones is so beautiful, their joints become a subject of admiration, and great part of the architectural ornamentation is in the beauty of lines of separation, drawn as finely as possible. Thus the separating lines of the bricks at Siena, of this gate at Lucca, of the vault at Verona, of this window at Orvieto, and of the contemporary refectory at Furness Abbey, are a main source of the pleasure you have in the building. Nay, they are not merely engravers' lines, but, in finest practice, they are mathematical lines--length without breadth. Here in my hand is a little shaft of Florentine mosaic executed at the present day. The separations between the stones are, in dimension, mathematical lines. And the two sides of the thirteenth century porch of St. Anastasia at Verona are built in this manner,--so exquisitely, that for some time, my mind not having been set at it, I passed them by as painted!