William built a large fleet and invaded England in September 1066, decisively defeating and killing Harold at the Battle of Hastings on 14 October 1066. After further military efforts William was crowned king on Christmas Day 1066, in London.
The official language spoken at the roman empire was the Greek language and the official religion worshipped there was Christianity of where Christian is short for Christianity which means follower of their founder Jesus Christ.
Yes, Kilwa was socially stratified.
The highest class was of the rulers who claimed direct Arab ancestry. They owned large plantations and controlled Indian Ocean trades.
The next was that of the Muslim-Swahili speakers who were mainly African. They were artisans and minor court officials.
The lowest class was of slaves who were non-Muslims. They worked on farms or estates or in production of cotton beads.