Monument Future - Siegfried Siegesmund

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       STUDY OF DECAY PATTERNS AND DAMAGE ASSESSMENT OF THE ACHAEMENIAN ROCK-RELIEFS OF NAQSH-E RUSTAM

      IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

       – PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

       VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

       Abstract

      Ancient rock reliefs in the necropolis of Naqsh-e Rustam (Iran) are important testimonies of the development of an outstanding monumental art over the centuries, in close relationship with their natural context. The rock reliefs underwent natural and anthropic decay processes in the course of time leading to the loss of fragments and in some cases to severe structural instability. This paper focuses on the oldest group of rock reliefs, dating back to the Achaemenian period; due to their location on the top of a sloping cliff, they are less accessible and more challenging by a conservation point of view. The reliefs have been studied in field and by means of a multi-analytical laboratory procedure, in order to identify the decay patterns, along with an assessment of the state of conservation. In order to frame the problem in a proper historical context, archival material including photographs, drawings and descriptions – created by western scholars between the 17th and the 20th century – were also analyzed focusing on any indications as regards deterioration problems. Fragments were studied by means of optical microscopy, SEM-EDX and XRD analyses. Among the main decay causes and mechanisms, the chemical dissolution of the stone substrate and the heavy microbiological subsurface growth play a major role. The layered aluminosilicate encrustations imply a continuous exposure of the limestone monument to the moisture ingress from the outer environment. Also, indications of the recent impact of atmospheric pollutants were observed, which is noteworthy, considering the distance of the monument from the urban areas.

      Keywords: damage characterization, decay pattern, Iran, rock relief

       Introduction

      Naqsh-e Rustam archeological site is located in Marvdasht municipal territory, in the Fars province, Iran (Figure 1). The site served as a necropolis during the Achaemenian (550–330 BC) and Sassanian (224–651 AD) periods (Schmidt 1970). Naqsh-e Rustam contains the rock-cut tombs of four celebrated kings of ancient Persia, Darius the Great, Xerxes, Artaxerxes, and Darius II.

      This paper deals with the conservation issues related to the outstanding bas-relief decorations of these tombs. During the recent years, reports about their progressive decay were repeatedly presented by local conservation experts as well as visitors. Different hypotheses were presented about the causes of threats and decay rates which may be 72put into two main classes. Those which relate the current situation of rock reliefs to the long-term exposure to the open-air weathering processes. On the other hand, it is argued that the rate of decay is drastically increased during the last decade due to anthropic factors such as air pollution, as well as climatic changes such as unexpected seasonal floods and land subsidence.

      Due to the difficulties in getting access to the tombs which are located in the upper parts of vertical cliffs, no report, mapping or analytical data was in hand about their previous state of conservation. Therefore, not only a close examination of the stone substance had to be done, but also it was necessary to obtain a clear picture of the state of conservation of the reliefs in the past decades or even longer periods, if possible.

      Another specific feature of these reliefs which were dealt with during the previous attempts for conservation in one of the tombs (Darius I) was the uncovering of polychromy. Therefore, it was important to consider the possibility of encountering such features also on other tombs and to discuss their decay problems as well. This study was carried out with the aim to support the decay mapping of rock reliefs, which can be used as a measure for systematic monitoring and mitigation of the risks in the framework of a preventive conservation program in the future. For this reason, a combined methodology consisting of different approaches were applied for data collection about the reliefs. In the meanwhile, it became possible to discover aspects of the original decoration, which was hidden for many years from the experts and visitors.

       Research Method

      Data were collected for this research through three approaches:

      a) Mapping the current situation

      b) Collection of historical data for assessing the decay phenomena in a time framework

      c) Sampling from representative points and analytical studies for understanding the decay

      The bas-reliefs are located at heights between 15 and 38 meters, on the perpendicular rocks. There-fore we inevitably required scaffoldings to gain access to the monuments. The local conservation teams had conventionally used rock climbing equipment under guidance of bouldering professionals for reaching the surface of interest. However, since 2018, scaffoldings have been mounted in front of the tomb of Xerxes, for preforming emergency conservation works.

      Figure 1: Map of Iran with the location of the site and rock-cut tomb of Xerxes in Naqsh-e Rustam and its bas-relief decorations.

      Close examination was done

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