The blocks of the lower courses are 1 ft. 10 in. high and from 4 to 7 ft. long; but towards the top of the dome the courses become gradually narrower. The floor of the vast chamber, which is entirely excavated, is the natural rock. A number of large stones, which have remained in the Treasury, make on travellers the erroneous impression that there is still a great deal of _débris_ left. From the fourth course of stones upwards there are visible in each stone two bored holes, and in many of these can still be seen remnants of bronze nails which, according to Sir W. Gell ("Argolis"), contain 88 per cent. of copper and 12 per cent. of tin. These nails, of which several have been found entire, had broad flat heads, and they can have had no other purpose than to retain the bronze plates, with which the whole interior was once decorated. We know by the testimony of the ancient authors that the Greeks in a remote antiquity ornamented their buildings in this manner, because in no other way can we explain the bronze houses and chambers which they mention.[136] [Sidenote: TREASURY AT ORCHOMENUS.] The only other example extant of walls which had once this kind of decoration is presented by the Treasury of Minyas in Orchomenus, which is built of beautiful white marble, but shows in other respects the very greatest resemblance to the Treasury of Atreus. It is constructed on the same principle, and appears to be of the same age and to have been erected for the same purpose. Each stone of this treasury likewise shows two or more holes, with frequent remnants of the bronze nails which once retained the brazen plates that decorated the inner walls of the edifice.[137] Thus it is certain that in a remote antiquity, before sculpture or painting came into use for wall decoration, polished metal plates were employed to give both splendour and dignity to the houses of the rich. In the Treasury of Atreus, the exterior of the door-lintel is decorated with two parallel mouldings, which are also carried down the jambs of the door. Above the lintel numerous holes can be discerned, to which bronze ornaments must have been attached. There are more such holes in the flat wall above the entrance, and all testify to the elaborate exterior ornamentation of the edifice. Above the entrance is an equilateral triangular niche, each side of which measures 10 feet. It is constructed like the triangular niche over the Lions' Gate; namely, the courses of masonry are shaped to the form of the niche, and it can have had no other purpose than to bear up the weight which would otherwise have pressed on the lintel.