عنوان مقاله [English]
Thermoluminescence (TL) dating was established in Oxford to fulfil the demand for dating ceramics and other heated man made products (Aitken, 1985). It determines the time elapsed since the mineral grains have been heated. Following the establishment of TL dating method, it was used to date fired materials such as pottery, flint and etc. Optically stimulated luminescence (OSL) determines the time elapsed since mineral grains have been last exposed to light just before burial (Aitken, 1989). Ancient walls are mainly built for defensive purposes. Some walls were destroyed and erected again and some had been extended. There is no accurate historical information about the time and purpose of the construction of the most of the ancient walls. Dating methods are key important tools in archaeological investigations. Absolute date for ancient building including walls, facilitate accurate time of construction and interpretation about the reasons that the monument was built. The proud history of association of TL and OSL dating with archaeology is well explained in literature (e.g., Roberts, R.G. 1997; Feather j. K. 2003); Monuments and settlements were also dated by TL and OSL including three Minoan palaces in Crete (Liritzis and Thomas, 1980); stoneware from the period of the early Thai kingdom of Sukhothai (Robertson and Prescott, 1987, 1988); the remains of the strategically-located Roman city of Carnuntum in Austria (Erlach and Vana, 1988); the Terracotta Army in Xi'an, China ( Lu et al., 1988); fifteen Mesolithic to medieval habitation sites in Denmark, Sweden and Finland (Mejdahl, 1989); the foundations of the archaic fortifications on Palatino Hill in Rome itself (Bacci et al., 1990); the Spanish exploration of western Canada in the 18th century AD (Williams et al., 1991); stone lines and cairns on the Arnhem Land plateau in northern Australia (Chaloupka, 1993); Mycenean wall in Greece (Liritzis, 1994); temples and citadels in Sri Lanka (Abeyratne, 1994); the temple of Apollo in Delphi (Liritzis et al., 1997); the archaeological sites of Tall Abu Fahd and Tall Qsubi in the Middle Euphrates Valley, in Syria (Sanchez et al., 2008); the city wall system of the oasis in NW Saudi Arabia (Klasen et al., 2011); the domed Stupas in Sri Lanka (Bailief et al., 2013). Following the explanation of basis of OSL dating, this article presents the application of OSL for dating Tammisheh wall in Iran, as a case study. The Tammisheh Wall in northern Iran was around 12 km long from the Elburz Mountains into the south- of the Caspian Sea and is lined by a fort in dry land in the south and another fort that is currently under water, in the north. A canal, conducted water along most of the wall. Tammīsheh Wall was in a good state of repair in the mid-7th century, because its inhabitants resisted against the powerful army of Sa‘īd b. al-‘Āṣ, son-inlaw of Caliph ‘Uthmān and governor of Kūfa, when it approached the Tammīsheh land corridor from the east in AD 650/651. (Sauer et al., 2014). The town of Tammīsheh continued to be occupied until at least the 13th. (Bivar and Fehérvári 1966). While Ibn Isfandiyār had attributed, the Tammīsheh to Peroz, Ibn Rusta (the early 10th-century author) suggested that the Tammīsheh Wall was built by Khusro I (AD 531–579). The Proposed dates, founder or period for construction of the wall is shown in Table 1. Until 2005, there had been no absolute date for the Tammisheh Wall. 14C is one of the most accurate methods but requires organic material. However, the wall is made of bricks that perfectly suits OSL dating. There are quartz and feldspar in the bricks. Quartz and feldspar are 2 main luminescence dosimeters. As bricks are cooked in ovens, the luminescence clock of quartz and feldspar inside the bricks will reset, due to temperature more than 300°C. The sediments contain quartz and feldspar. When sediments are exposed to day light, their luminescence clock will reset. The luminescence clock will start again as soon as bricks cool down or the sediment that was exposed to light is buried. Therefore, we employed both OSL and carbon fourteen methods. We collected one OSL sample sediment below foundations of Tammisheh Wall (Fig 4) which unfortunately overestimated the real age. We also sampled one OSL sample and a charcoal from a preserved section of the kiln in Trench F (Fig 8). Another OSL sample and three radio carbon samples were collected from the trench “O” of Bansaran fort (Figs 14-17). All samples were transferred and dated in Oxford. The dating result of samples is presented in Table 1. The result of OSL and 14C ages proved conclusively that Tammisheh wall and Bansaran fort had been built during the Sasanian period.