The "wooden walls" that were supposed to protect Athens from the Persians and that the Oracle of Delphi prophesied were, of course, the ships, as Themistocles said, but the walls of the Acropolis, the oldest preserved on the Sacred Rock, have protected it from enemies for centuries. Sometimes parts of it were destroyed and enemies invaded, sometimes small parts collapsed or toppled over without human intervention, sometimes rainwater or a sewer caused damage. For the walls there is now a separate master plan, the implementation of which will begin after the approval of the Central Archaeological Council.

The historical collapses of parts and the constant repair works are the main evidence that the ancient walls, despite their careful construction, had structural problems and in some cases failed under heavy loads (earthquakes, earth tremors). In the areas where they have been preserved, they have been severely deformed. An example is the deviation of the south wall in the corner SW of the Parthenon to the outside.

On parts of the walls, warping and protrusions can still be observed, probably due to earth tremors, the detachment of the newer installations or problems with the foundations (slipping, overloading).

The movement of water is perhaps the most important factor in the wear and tear of the walls. For decades it was on the surface until drainage works were recently carried out under the direction of Michalis Lefantzis. The water was stored in large quantities in the embankments, which increased the pressure forces. It gradually evaporated causing corrosion, and eventually flowed to the surface of the rock, causing problems in the foundation. The heavy dampness in places showed that the water had penetrated the masonry, causing severe decomposition of the rock.

Collapse of the section

According to an earlier study by Manolis Korres, Chairman of the Committee for the Preservation of the Monuments of the Acropolis, and Petros Koufopoulos, "the corrosion and deterioration of the ancient wall, with a simultaneous reduction in its mechanical properties, led to the collapse of sections of the wall. These sections were built in different eras with different materials and techniques than the ancient building. The new buildings had smaller dimensions than the original, and less mortar was also used.

Parts of the new additions collapsed after corrosion and deterioration of the mortar, and new additions were built, so that the wall on its exterior shows a variety of techniques and building materials, both in its composition and geometry. Great damage was also caused by shelling, which created gaps in the wall and loosened its structure.

Extensive works to the major restoration works by N. Balanos were carried out to secure and protect the wall, especially on the south side. The high walls were built with small-sized stones and mortar binder. The deterioration of the mortar has meant that the outer wall on the south side is now at the limit of equilibrium in some places and in danger of collapse, posing the risk of chain collapse of the buildings above, as well as general stability problems of the old wall. In the areas where buildings have been detached, it can be seen that the external extension has been connected to the old wall with mortar. The deterioration of the mortar mainly means that today there is no adhesion (connection) of the external extension with the old internal wall.

From the classification made, it appears that there is an increased risk of rockfall on the northern slopes. The most critical are the areas of the south wall with the large slope heights and an area with retaining wall function.

From Mycenaean times

The study also draws on the report of special expert Mairis Ioannidou, who served as director of the Acropolis Monuments Maintenance Service, and notes that the Acropolis was first built in the 13th century.

Parts of this fortification probably remained until the Persian Wars, when the sanctuaries and walls of Athens were destroyed by the Persians. After the return of the Athenians, construction of new walls began. Under Themistocles, the northern wall was built first, while a little later, under Kimon, the eastern and southern walls were built with the spoils of the victory at Eurymedon river(469 or 466 BC).

The western approach lost its fortified character with the construction of the Propylaea in 437-432 BC. This side was fortified in the late Roman period, probably after the Heruli raid in 267 AD. At that time or a little later, the eastern part of the northern wall is rebuilt and the northernmost part of the eastern wall is completed.

During the Byzantine period, the same defense system was probably maintained without any particular changes. In the Frankish period (1204-1456), a tall rectangular tower was built on the south of the Propylaea, while the west side seems to have been generally reinforced. In Ottoman times (1456-1833) the walls were adapted to the requirements of firearms and further strengthened, especially on the west side.

Extensive repairs and rebuilding were apparently required after the 1705 earthquake, and fighting during the Greek War of Independence also caused severe damage. In 1834, it was decided to remove the walls "without archeological or historical value" and the systematic demolition of the medieval and Ottoman phases began (demolition of the western fortifications and ramparts).

In the first half of the 20th century, repair works were carried out by Balanos (1899-1938) and Orlandos (1947-1949) which aimed primarily at fixing structural and static problems.

The architect Chr. Pinatsis states in the same study that each construction phase "expresses the way the corresponding era dealt with the defensive needs of the most important sanctuary and fortress of the city, and the damages are often linked to the results of the battles fought for its restoration, including those of the War of Independence".

Palimpsest

The Acropolis Wall is described as "a unique monument, where the palimpsest of successive construction phases has not only been preserved, but also supplemented by new constructions, without the intention of restoring the original form. Because of their fortification and their static function, the walls become first and foremost a bearer of historical memory". However, without "ceasing to shape the environment of the great temples of the Acropolis".

Structural problems refer to inherent problems of the structure (material, rock, method of support) that manifest themselves in different ways (cracks, deviations, subsidence, collapses). A structural problem is found more or less on the entire south wall, which is also confirmed by the older interventions and led to the support with columns and the lining of entire areas. The structural problems are mainly related to the action of water and humidity, which leads to corrosion phenomena, especially on the north wall (from superficial wear to complete dissolution and detachment of parts of the stone). Problems also occur with the fillings, the situation being aggravated by the use of cement mortar.

In this broad context, the restoration of the classical structure is proposed in three cases: A) islands of recent masonry and/or small-format mortar of the 20th century, which have replaced mainly the surface of individual plinths or groups of stones (in some places along the entire north wall, in the SE corner and in some places of the wall).

B) Extensive annexes, of which enough parts of classicism are preserved on both sides, which were clearly continuous

C) Areas adjacent to the classicist, where the ancient structure is preserved behind the adobe construction and sporadically on the facade.

As for the southern wall, the reconstruction of the classical structure is generally not proposed (it would affect the entire area of the classical wall), due to the reservation of smearing an extensive historical/architectural phase, the extent of the intervention, the need to preserve the remarkable medieval structures, and various other structural problems. Here, grouting and local additions with earthen constructions of the Ottoman and more recent structures are proposed. Restoration of the old masonry is proposed in the SE corner,and in the area west of the 13th column. Finally, it is proposed to remove the Balanos lining at the western end of the wall and restore the original form along a length of 12 meters.