Tahirids and Zaydis, 9th Century CE
In 195 H (811 CE), Ray stood at the frontier of the territories of Harun's sons, Caliph Muhammad ibn Harun al-Amin and governor Abu Jafar al-Ma'mun ibn Harun. Their advisors had goaded them into war, and when al-Amin's forces, led by former Ray governor 'Ali ibn 'Isa ibn Mahan, marched over the Zagros Mountains from Baghdad, a much smaller, but mobile and well-led defence force, under Tahir ibn al-Husayn, awaited them at Ray. Tahir decided to risk meeting the invaders out on the plain, where his cavalry could be most effective, so the Battle of Rayy, brilliantly successful prelude to his counter-invasion of Iraq, actually took place about a day's march from the city. When al-Mam'un was thus established as Caliph, Tahir was rewarded with his old governorship of the eastern territories, which continued in the family for decades as a hereditary post.
In 250 H (864 CE) the people of western Tabaristan had had enough of the growing arrogance and corruption of the Tahirids, and appealed to al-Hasan ibn Zayd of the Alavid dynasty, a leader of the Zaydi Shi'ites, who lived in Ray. He agreed to help, and was soon acknowledged as lord of Tabaristan, with the backing of nearly all the other peoples of the Elburz Mountains, including the Daylamites. An Alavid, Muhammad ibn Ja'far ibn al-Hasan, expelled the Tahirid governor of Ray in the winter of 250 H (865 CE), but Muhammad ibn Tahir sent a force from Khorasan, led by Muhammad ibn Mikal, which soon retook the city and captured Muhammad ibn Ja'far. In the same period of counter-attack, al-Hasan himself was forced to withdraw to Daylam, but quickly regained his position with the Daylamites' help. The Daylamite general Wajin recaptured Ray, and installed Ahmad ibn 'Isa ibn 'Ali as governor. In 252 H (866 CE), we learn of Ahmad recapturing Ray from the Tahirid governor 'Abd Allah ibn 'Aziz with the help of the Daylamite prince Justan ibn Wahsudan, so presumably he was expelled at some point. Abd Allah later turned the tables and captured Ahmad, but was himself subsequently taken prisoner by al-Qasim ibn 'Ali ibn al-Hasan for the Alavids. In 253 H (867 CE) Musa ibn Bugha al-Kabir was appointed by the Caliph as governor of Jibal, with a mandate to recover Ray from the Alavids. This he did, but in the summer of 255 H (869 CE) he had to go to the Caliph's capital at Samarra, and apparently left 'Abd al-'Aziz ibn Abi Dulaf in charge at Ray. "Apparently", because all we know about 'Abd al-'Aziz' tenure is that when al-Qasim arrived at the city gate a year or so later, sent by al-Hasan, it was 'Abd al-'Aziz who officially invited him and his troops in. Musa rushed back from Samarra as soon as he heard the news, in late summer 256 H (870 CE) and soon ousted the Alavids. They reportedly took over again for a short while in 258 H (872 CE), and the whole region was becoming so troublesome that in 259 H (874 CE) Musa resigned his governorship. About this time, incidentally, Khalaf al-Hallaj was sent to spread the message of Isma'ili Shi'ite Islam across the plain of Iran, as the first da'i of Jibal, based near (later in) Ray.
Musa's appointee as governor at Ray, al-Salani, died in 262 H (late 875 CE), and for political reasons, the Caliph appointed as his replacement the Iranian ex-bandit Ya'qub-i Laith Saffari, who in 259 H (873 CE) had destroyed Tahirid power in Khorasan. Ya'qub, first of what would become the Saffarid dynasty, had coins minted at Ray within months of taking office (though his capital was further east, at Zaranj). Ya'qub died in 265 H (879 CE) and was succeeded by his brother Amr-i Laith Saffari. In 270 H (884 CE) al-Hasan died, and the following year, the governor of Qazwin, Adgu-tegin, seized Ray, which apparently had been taken over by al-Hasan's Alavid supporters. About the same time, precisely because the threat from rebels was diminishing, the Caliph turned against 'Amr, favouring instead Ahmad ibn 'Abd al-'Aziz ibn Abi Dulaf, governor of Isfahan (and son of the former negligent Ray governor). While Ahmad harried 'Amr in the west, a Tahirid supporter, Rafi' ibn Harthama, was attacking his possessions in the east, in alliance with the rival Samanid dynasty. Moving steadily westward, in 275 H (888-9 CE) Rafi' defeated al-Hasan's brother and heir Muhammad ibn Zayd, then he captured Ray in 276 H (889 CE), and made it his headquarters.
A new Caliph, al-Mu'tadid, brought a new policy in 279 H (892 CE)- he saw Rafi' as a greater threat than 'Amr, so he sent Ahmad to eject him from Ray. This was achieved with ease, in a battle near the city on 23 Dhu al-Qadah (14 February 893 CE)- though it would be another three years before Rafi's career was finally ended, by 'Amr. Meanwhile, the Caliph's son, al-Muktafi was temporarily installed as governor of Ray. The Caliph ingeniously rewarded 'Amr's success against Rafi' in 283 H (896 CE) with a grant of the governorship of Ray plus large territories to the east. In order to claim his reward, 'Amr had only to persuade the incumbent Samanid governor of the eastern territories, Isma'il ibn Ahmad ibn Asad, to leave. The first army he sent failed, so he decided to take charge of an invasion in person, resulting in his capture and humiliation in 287 H (900 CE). Isma'il was rewarded by having his own territory expanded to include the other lands that would have been 'Amr's, including Ray. Also in that year, the Samanids gained control of Tabaristan.
Read more about this topic: Military History Of Ray, Iran