Experts are working to decipher a newly discovered inscription unearthed in an ancient necropolis near Persepolis, an official of the Cultural Heritage Organization of Iran, said on Monday.

The inscription which dates from the Sassanian period (224-651 AD) was found in Naqsh-e Rostam and is written in Pahlavi language (also known as Middle Persian) which was the official language of the Sassanian Empire.

Naqsh-e Rostam, the site where the inscription was found, was a necropolis and religious center about 12 km northwest of Persepolis, the ceremonial capital of the Achaemenid Empire (550-300 BC). However, some of the relics on the cliffs may date as far back as the Pre-Iranian Elamite Period (2700-539 BC).

Four huge tombs from the Achaemenid period, including the tomb of King Darius the Great (550-486 CE) hewn into the cliff face and a square-shaped building made with stone blocks from the Sassanian which may also have had a significance in burial rites are among the most important relics of the necropolis.

Several inscriptions and reliefs of Sassanian kings including a rock relief showing the Sassanian king Shapur I on horseback, with the Roman Emperor Valerian bowing to him in submission, are among the other significant surviving relics of Naqsh-e Rostam.

Despite the huge importance of the ancient necropolis, unlike Persepolis and Pasargadae, the capital of the Achaemenid Empire under Cyrus the Great (559-530 BC), Iran has not been able to list it as a UNESCO Heritage Site due to the failure to meet the requirements of UNESCO as to measures taken for the preservation of the site and documentation.

Officials say the inscription is being deciphered. But reading Pahlavi texts is no easy task.

An Aramaic-derived alphabet was used for writing in Pahlavi. The script is very difficult to read due to the use of heterograms. The heterograms were words written in Aramaic but read as their Middle Persian equivalent. It is similar to writing eg in English and reading it "for example".

In addition to the use of heterograms, the variations of the alphabet between the ordinary script used on parchment and the version used in inscriptions make reading Pahlavi inscriptions which are often badly damaged by exposure to the elements even more complex.

In the past couple of decades, the decline of groundwater tables which has resulted in sinking ground has seriously damaged the relics in Naqsh-e Rostam or put them in danger of further deterioration. Critics of the Islamic Republic say the government does not put enough effort into the preservation of pre-Islamic relics.