Can you check these sentences for me, please?

1)He is a superstar now and he is slamming (a synonym?) on his guitar.
2)He is responsible for the building (?) of Westminster Abbey.
3)He withdrew from Britain to defend Rome against (or from?) a Barbarian attack.
4)According to the medieval mind, the life of the soul was the real one, whereas life on earth was just a preparation for it.
5) According to the Ptolemaic theory, the earth is at the (?) centre of universe with the planets moving in circular orbits around it.
6) Some Germanic tribes invaded Britain after the retreat of the Romans. They gave the land the name England.
Thank you

1. strumming, playing

2. construction
3. against or from
5. why the question mark?

Sra