kingdom of Parthia, which covered present-day Turkmenistan and Iran. The Parthian kings ruled their domain from the city of Nisa – an area now located near the modern-day capital of Ashgabat – founded by Arsaces I (reigned c. 250–211 BC), and was reputedly the royal necropolis of the Parthian kings, although it has neither been established that the fortress at Nisa was a royal residence nor a mausoleum. Excavations at Nisa have revealed substantial buildings, mausoleums and shrines, many inscribed documents, and a looted treasury. Many Hellenistic art works have been uncovered, as well as a large number of ivory rhytons, the outer rims decorated with Iranian subjects or classical mythological scenes. During the 4th to early 7th century CE, much of the population was already in settlements around the fertile river valleys along the Amu Darya, and Merv and Nisa became centers of sericulture (the raising of silkworms). A busy caravan route, connecting Tang dynasty China and the city of Baghdad (in modern Iraq), passed through Merv. Thus, the city of Merv constituted an important prize for any conqueror. Arab conquests and Islamization Central Asia came under Arab control after a series of invasions in the late 7th and early 8th centuries and was incorporated into Islamic Caliphate divided between provinces of Mawara'un Nahr and Khorasan. The Arab conquest brought the religion of Islam to all of the peoples of central Asia. The city of Merv was occupied by the lieutenants of the caliph Uthman ibn Affan, and was constituted as the capital of Khorasan. Using this city as their base, the Arabs, led by their commander Qutayba ibn Muslim, brought under subjection Balkh, Bokhara, Fergana and Kashgaria, and penetrated into China as far as the province of Kan-suh early in the 8th century. Merv achieved some political spotlight in February 748 when Abu Muslim (d. 750) declared a new Abbasid dynasty at Merv, and set out from the city to conquer Iran and Iraq and establish a new capital at Baghdad. Abu Muslim was famously challenged by the goldsmith of Merv to do the right thing and not make war on fellow Muslims. The goldsmith was put to death. In the latter part of the 8th century Merv became obnoxious to Islam as the centre of heretical propaganda preached by al-Muqanna "The Veiled Prophet of Khorasan". Present Turkmenistan was ruled by Tahirids between 821 and 873. In 873,