Pietro I's conciliating policy towards the Empire was ineffective. After having ruled Venice for four years, Pietro I voluntarily abdicated to become a monk, allowing the pro-Ottonian Vitale to return to Venice as Doge in 977, restoring the city's friendly relationship with the Empire. However, Vitale's reign was short (less than two years) and he too voluntarily abdicated to become a monk. With the position vacant, the pro-Byzantine Tribuno Memmo became the new Doge in 979. With the change in leadership, Otto II was reluctant to renew the city's commercial agreements which his father had previously granted to the city. It was only after the intervention of Otto II's mother, the dowager empress Adelaide of Italy, that the Emperor renewed the agreements.