Complex sentence: Fortresses such as Marvão thus acted to deter spring offensives against the Banu Marwan from the Emirate in Córdoba; such offensives were common against another muwallad rebels, notably those against Umar Ibn Hafsun, based in Bobastro near Ronda.
Split into simpler sentences: Fortresses such as those at Marvão would now deter any spring offensives against the Banu Marwan from the Emirate in Córdoba. These offensives by the Emirate were common against another rebellious muwallads, notably those against Umar Ibn Hafsun, based in Bobastro near Ronda.