Answer:
Papal coronations were held at the basilica, and in 800, Charlemagne was crowned emperor of the Holy Roman Empire there. In 846, Saracens sacked and damaged the basilica. ... In response Pope Leo IV built the Leonine wall and rebuilt the parts of St. Peter's that had been damaged.
He wanted to Russia to have a warm-water port ( a port that ships could use even in water. He wanted to expend Russian power beyond Moscow. He wanted to mark his legacy by building a magnificent new city