How does the story relate to Judism, Christianity, and the Roman Empire? Also, what do you think happens between Daniel and Thacia after the end?

The story has everything to do with Judaism, Christianity, and the Roman Empire.  The Jews hated and suffered under Roman Rule as is evidenced by the deaths of Daniel's uncle and father by crucifixion.  The Jews were waiting for a biblically promised Messiah to free them from Roman rule.  Most looked for a kinglike messiah who would lead an army to defeat the Romans.  This is what Daniel saw in Rosh.  They were bound together by their hatred of the Romans and worked as an army to defeat them.  However, Rosh was not moral in the Jewish sense of the word.  He did not follow the Jewish laws.  He steals, lies and cheats. 

Jesus represents the other side of the Messiah as presented in the Old Testament.  He preaches that love is the way to gain the Kingdom of God, not war.  He reaches out in love to those who are not Jews breaking the prejudices of Jews against gentiles.  Unlike, Rosh, Jesus acts selflessly and keeps the spirit of the law as presented in the scripture.  He heals the sick, gives to the poor, is kind to the needy, and acts as a servant in all situations.  He shows that hate can never gain anything.   At the end of the novel, Daniel sees that Jesus, not Rosh has the answer.  The split between Rosh and Jesus represents the later split between the Christains and the Jews.  The novel shows how they come from the same place but part along the way.