 The Barmakid family played a decisive advisorial role in establishing the Caliphate, but declined during Rashid's rule.Al-Amin received the Caliphate from his father Harun Al-Rashid, but failed to respect the arrangements made for his brothers, leading to the Fourth Fitna.Al-Ma'mun's general Tahir ibn Husayn took Baghdad, executing Al-Amin.