Although big Shi'a academies existed in Qom dating back as early as 10th century CE, the hawza of the city became prominent at the time of the Safavids when Shi'a Islam became the official religion of Iran. The famous teachers of that era included Mulla Sadra and Shaykh Bahai. The modern Qom hawza was revitalized by Abdul Karim Haeri Yazdi and Grand Ayatollah Borujerdi and is barely a century old. There are nearly three hundred thousand clerics in Iran’s seminaries. At present Grand Ayatollah Hossein Vahid Khorasani heads Seminary of Qom.