fall of the Parthian Empire, and the rise of the Persian Sassanid Empire, Zoroastrianism was chosen as the state religion, and the city of Semnan was once again brought under the reign of Persian customs and traditions. Post-Islamic Era After the Muslim conquest of Persia, the religion of Islam was established within the city of Semnan. Though, unlike modern day Semnan, the people of the city originally practiced Sunni Islam, similar to the rest of early Islamic Persia. However, the institution of Sunni Islam did not last very long. The Alavids of Tabaristan had established a Shi'a Islamic emirate and upon conquering Semnan, brought the Zaidi Shi'a sect of Islam. Then, in the year 427 AH, the Seljuq Turks invaded and devastated the city. Nevertheless, it was the very Seljuq Turks that built many of the historical monuments and infrastructure of medieval Semnan. As the Seljuq Empire grew weak, the Abbasids managed to reconquer and assert their sovereignty over Persia. The people of Semnan suffered severely under the Abbasid Caliphate. It is possible that the years of Abbasid rule traumatized the people of Semnan, and even to this day, the Semnani people despise the color black because of its utilization for the black flags of the Abbasid Caliphate. The Abbasid rule was ended by the brutal, devastating invasion of the Mongols in the year of 618 AH. The Mongol hordes massacred the people and burnt much of the city to the ground. Semnan would not recover until the rise of the Turco-Persian Safavid dynasty. The Safavids brought the Twelver Shi'ism sect of Islam to Semnan, and contributed to the reconstruction of the city. Qajar Era With the rise of the Qajar dynasty, historical Semnan witnessed economical, cultural, infrastructural, and political progress. The very tribe that rose into becoming the Qajar dynasty was based out of the mountainous terrain between modern-day Semnan, Mazandaran, and Golestan. The Qajars turned Semnan into a civil fortress, from which they oversaw the major trade route between their capital in Tehran and the holy city of Mashad. In addition to infrastructural growth, some Qajar royals built their estates in the city. Semnan was also an important medical center for members of the Qajar Imperial Family and was home to many notable physicians and doctors of the era. Economically, the city consisted of several feudal estates with agricultural plantations which relied on serf labor. Pahlavi Era The