The upper storey was originally of wood, and was destroyed by a great fire caused by lightning, in the time of the Emperor Macrinus; it was rebuilding of stone during the whole reign of Alexander Severus, and was completed by Gordianus III., who commemorated it by a medal, taking the credit of the rebuilding to himself. There was a row of columns in front of the upper gallery; two of the bases remain there, and a number of capitals that belonged to that colonnade[13] have fallen down in an earthquake, and are now lying about on the ground on the level of the arena, but were found in the substructures. These are very rude workmanship[14], perhaps only because they were to be seen from a great distance, but they may possibly have been preserved from the works of Scaurus; they are very different from the finished capitals used in the lower gallery. This rebuilding and addition of the upper storey alone took twenty years in a great building era. Great changes were made at that time to raise the upper storey securely, and this we have pointed out. It is seen that the builders had no faith in the soft tufa for carrying any considerable weight, and provided piers of the hard travertine at short intervals for that purpose[15]. There are altogether six storeys in the present building, but three of them may be considered as _entresols_ for passages to and from the _vomitoria_[16]. Gordianus also rebuilt the front of one bay of the lower storey, which had probably been damaged by some of the burning timber falling in front of it. At the bottom of the great central passage was found a very remarkable wooden framework, resembling what is usually called a cradle in a dockyard, and used for a vessel to stand upon[17]. This cradle had the appearance of having been burnt, but it is known that long exposure to extreme moisture will give the same appearance to wood that burning it does. At the east end of the passage, at the lowest level, is the great drain, half above and half below the level of the old pavement[18]. At the entrance to this are the grooves of a sluice-gate in the walls on each side, and an original iron grating to prevent anything being carried through by the rush of water; by this it is evident the water was let off from the canals from time to time through this drain. Unfortunately the old drain, which was at a great depth, was so much damaged that it was found impracticable to repair it, though it was traced the whole length of the building, as far as the Arch of Constantine at the opposite end[19].