Many Arab, Turkic, and especially Mongolian and Afghan tribes have brought great changes in the language, ethnicity and culture of the people each in their own time. Surprisingly, Mashhad enjoyed relative prosperity in its economy in the Mongol period. Mashhad is famously known as the city of Ferdowsi, the Iranian poet of Shahnameh, which is considered to be the national epic of Iran. The city is the hometown of some of the most significant Iranian literary figures and artists such as Mehdi Akhavan-Sales, the famous contemporary poet, and Mohammad-Reza Shajarian, the traditional Iranian singer and composer. Ferdowsi and Akhavan Sales are both buried in Tus, an ancient city that is considered to be the main origin of the current city of Mashhad. On 30 October 2009 (the anniversary of the death of Imam Reza), Iran's then-President Mahmoud Ahmadinejad declared Mashhad as "Iran's spiritual capital".^[4][5]