Conservation problems

1. The massive concrete structures and the republican tuffs The area of the excavations near the Magna Mater Temple,
   
   
   Fig. 1: Excavations near the Magna Mater Temple
   
   in the upper part of the Palatine Hill, is supported by a high substruction wall (about 30 m), which goes from the south west border of Domus Tiberiana to the end of the hill.
   
   
   Fig. 2: High substruction wall in the south-west side of the Palatine Hill
   
   
   The construction material is a Roman concrete with a lime and pozzolana mortar binding black pieces of flint.
   The wall was built in part on a previous republican structure (made with regular tuff blocks) and in part directly on the original Palatine tuff.
   The wall shows a diffuse surface decay and vertical cracks which causes worrying about its stability.
   The vertical cracks extend from top to bottom (fig. 4) and clearly show structural choking, probably due to different ground sinking. The possible widening of the cracks and slits, and the eventual rotation of the resulting wall portions should be monitored in order to check the wall stability. It is important to underline that the collapse of this wall would be disastrous for
   all this part of the Palatine Owing to the fact that the concrete structure is partially founded on rocks and tuffs of various origin and composition, special attention is to be given to the present poor conservation characteristics of such rocks and tuffs (masonry slits and cracks are clearly visible). In fact, in the central part, the substruction wall was built on a previous foundation structure made of huge tuff blocks (fig. 5). Some of them were stolen in the past to be used again as construction materials in other buildings, so creating wide openings and spaces inside the original
   foundation. The leaching of such porous tuff materials is accelerated by the continuous water supply from the upper levels, where no draining system exists. Moreover, previous important archaeological excavations on the top of the hill (fig. 1) act as a funnel for the penetration of rain water which then impregnate all the lower walls and substructions.
   The water carries soluble salts such as sodium and potassium sulphates (but also calcium sulphate) to the exposed surfaces, where they crystallize producing a progressive disgregation of the mortars. Such phenomenon concerns all original foundation rocks and many tuff blocks of the previous walls (fig. 6); it is active as well on the roman concrete were the pozzolanic mortar and the tuff "caementa" are progressively attacked and dissolved, while the flint (siliceous aggregate) is little by little secluded and falls. The progressive soaking of the concrete walls is clearly visible (lower dark parts) in figure 7.
   The tuffs blocks of the previous substruction (supporting the concrete walls) belong to two main types: a red tuff which includes volcanic black stones (Fidene tuff), and a yellow tuff from Grotta Scura. The red tuff decay produces relatively big chips; while the yellow tuff easily passes to the powdered state. Both materials are attacked by the environmental agents, though the first one is more resistant.
   In the same area there are remains of the original gray tuff from which this part of the Palatine Hill was made. Moreover, other walls made of archaic tuff blocks are visible.
   
   
2. The republican wall and the red tuff nearby Just besides the previously mentioned area, there are the remains of an important Republican wall
   
   
   Fig. 3: Republican tuff wall near the high substruction wall shown in fig. 2
   
   made of red tuff blocks laid on a layer of yellow soft tuff; the latter has been exposed to the environmental agents by former archaeological excavations. Consequently, the lower and weaker yellow tuff is rapidly eroded (the resulting powder is visible at the base) so that the dimension of the support for the upper part of the wall is decreasing.
   
   
   Fig. 8: The erosion of the Republican wall
   
   Behind the republican wall, on the slope to the top of the hill there is a bench of red tuff (tufo lionato) which is an original constituent of the Palatine Hill. Cracks and detached parts of the rock are clearly visible: the past restoration works were limited, insufficient, and in many cases destroyed.
   
   
3. South slope of the main concrete wall The south slope, respect to the huge above-mentioned wall, ends (before the republican wall) with a natural terrace.
   On its turn, this terrace is limited by a Roman wall made by concrete (foundation) and by red tuff (upper part): the tuff has no regular size and dimension (probably recovery material) and is kept in position by alternating layers of bricks. The wall is very badly conserved due to the decay of the tuff and of the mortar, caused by the action of the soluble salts. The erosion of the foundation is reducing the support for the wall.
   The hill slope becomes particularly sharp and ends, at the top, with a number of masonry remains in precarious equilibrium (fig. 9). The cutting of bushes and trees (necessary for other reasons) has weakened the soil resistance so that the action of rain water could be now very dangerous.