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| Intervention Principles |
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The intervention principles regarding the preservation of Jerusalem's city wall were drawn up in order to ensure a professional and controlled conservation process. The principles will direct the intervention measures which aim to conserve the historic, aesthetic and technological values of the monument, in accordance with the Israel Antiquities Authority policy for the conservation of built heritage.
1. Documentation and Survey
Documentation and survey are an inseparable part of the conservation process. They constitute the basis for decision making with regards to the manner of intervention.
1a. The entire length of the city wall was measured by means of a laser.
1b. Three general surveys were conducted: a historical and urban survey; a physical-engineering survey and a natural resource and environmental survey.
1c. A survey and detailed documentation will be done for each section of the wall.
The survey and documentation will touch on the following aspects: historical, urban, architectural and physical-engineering prior to the treatment.
1d. The intervention will be documented in detail.
2. Respect for the Existing Material
The principle of respecting the original material will be a fundamental guideline in the treatment of the wall. The remains will be conserved, without loss of evidence or information. The intervention will be done by non-estructive means. Any deviation from the principle of respecting the existing fabric requires special justification.
2a. The stones in the wall that are subject to destructive processes will be conserved in their current condition, unless they have lost their constructive function, in which case they will be replaced with new stones that match the original.
2b. The original mortar that has not deteriorated will be preserved.
3. Minimal Intervention
The replacement of stones in the wall will be limited to the necessary minimum, in recognition of the importance of the original in situ fabric to the authenticity of the monument.
3a. Every effort will be made in order to stabilize the damaged stones and leave them in situ.
3b. Completing architectural elements will be limited to the necessary minimum. The completion will be executed in regions where later additions and changes spoil the architectural wholeness of the wall. This will be done on condition that the existing changes do not bear any evidence of important historical developments.
4. Building Technology
Preference will be given to the use of traditional technology and original materials. New materials will only be utilized after the material has been tried and it has been ascertained that it will not cause damage and will not prevent or hamper future "retreatability".
4a. The replacement of stones or the completion of missing stonework will be done utilizing stone that is indigenous to Jerusalem or its environs, and which was commonly used in the walls.
4b. The mortar in the joints will be lime-based.
4c. Stainless steel or fiberglass pins will be used to secure the stones in place.
5. Reversibility
All intervention will be done using materials that match the original fabric and in a manner that is as reversible as possible.
6. Discernible Intervention
The intervention will be discernible from the original remains. The intervention will be marked in a subtle manner so as not to be conspicuous in the appearance of the original wall.
6a. Each new stone will be marked with a seal for the sake of identifying it in the future.
6b. A new stone that will be installed in the wall will be marked with a registration seal that bears the symbol of the Israel Antiquities Authority on a lead or tin casting, drilled in the stone. The casting will not exceed 18 mm in diameter and the drilling will not be more than 50 mm deep. The drilling's location will be fixed in the lower right hand corner of the stone.
6c. In places where a number of stones will be replaced in sequence - in the case of completing a wall for instance - the line of the reconstruction will be marked by means of a brass corner which will clearly indicate that the courses above the corner are new/restored construction. The symbol of the Israel Antiquities Authority will be stamped on the corner. The outer dimensions of the corner will not exceed 20 x 20 mm.
6d. The mortar used to point up the joints will be a shade of gray so as to be distinguishable from the colors of the existing mortar in the wall.
7. Conserving the Architectural Value
In the conservation action we will strive for intervention that will be carefully integrated, in a manner that will not be noticed in the texture and appearance of the wall - the shade of the mortar and the kinds of stones that it is composed of. The manner of the intervention in each section of wall will be uniform, in accordance with the recommendations of the physical-engineering survey.
7a. The top of the crenellations or the original height of the top of the wall will be sealed using lime-based mortar that is applied in the shape of a flattened dome. The sealing mortar will be made smooth and will drain water toward the outside of the crenellation.
7b. A crenellation or section of the top of the wall that is architecturally incomplete will be sealed using lime-based mortar together with flat stones. This specification will express the core of the wall.
7c. The new mortar that will be applied in places where a large amount of the ancient mortar survived will be integrated as much as possible in the shade and texture of the original material.
7d. Mortar finish specification: mortar that is used for pointing up the joints will be applied in a smooth and slightly depressed manner, c. 5 mm below the surface of the stone.
7e. Stone dressing finish specification: the finish of the new stone will be mutba - a delicate kind of stone dressing done with a hammer.
7f. The finish treatment of the new stone will include rinsing it in acid to create a slightly coarse surface.
8. Architectural Restoration
8a. The wall's crenellations will be completed based on a number of criteria, including:
- The disturbance it causes to the skyline.
- To what extent can the crenellations that are missing stones be seen.
- Missing stone mass. Stonework will not be completed when more than 35% of the crenellation stones are missing in a certain section of the wall. In this case a minimal amount of stonework will be supplemented, the aim of which is to reinforce the cadence of the crenellations.
- Preference will be given to the architectural restoration of the crenellations in the gates and towers that are visible from different vantage points. This in order to emphasize the aesthetic value of the architectural components which standout along the course of the wall.
Note: the intensive use that was made of cement-based mortar, which has its origins in earlier measures to rehabilitate the wall, is irreversible. Due to the anticipated damage to the wall's stones as a result of removing them and the cost/benefit considerations, it was determined that the later mortar that is well preserved will not be replaced.
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