Complex sentence: At this time, Leo put an end to the attempts of the Ravenna archbishops to get away from the control of the Bishop of Rome, but also abolished the tax it had been customary for them to pay when they received the pallium.
Split into simpler sentences: At this time, Leo put an end to the attempts of the Ravenna archbishops to get away from the control of the Bishop of Rome. The Pope sweetened the deal for the Ravenna bishops by abolishing the tax it had been customary for them to pay when they received the pallium.