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. STUDY OF DECAY PATTERNS AND DAMAGE ASSESSMENT OF THE ACHAEMENIAN ROCK-RELIEFS OF NAQSH-E RUSTAM Sahar Ahmadinezhad 1 , Antonio Sansonetti 2 , Andrea Pane 3 , Danilo Biondelli 2 1 Polytechnic University of Milan, Dep. of Architecture and Urban Studies (DASTU), Milan, Italy 2 Institute of Heritage Science (ISPC) Italian National Research Council (CNR), Milan, Italy 3 University of Naples Federico II, Architecture Dep.(DiARC), Naples, Italy aluminosilicate encrustations imply a continuous exposure of the limestone monument to the mois- ture 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 prov- ince, Iran (Figure 1). The site served as a necrop- olis 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 re- lated to the outstanding bas-relief decorations of these tombs. During the recent years, reports about their progressive decay were repeatedly pre- sented by local conservation experts as well as vis- itors. Different hypotheses were presented about the causes of threats and decay rates which may be Abstract Ancient rock reliefs in the necropolis of Naqsh-e Rustam (Iran) are important testimonies of the de- velopment of an outstanding monumental art over the centuries, in close relationship with their nat- ural 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 proce- dure, 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 caus- es and mechanisms, the chemical dissolution of the stone substrate and the heavy microbiological subsurface growth play a major role. The layered Siegesmund/Middendorf – Monument Future