Questions about sentences in 三国演义

[vn.haint]

I'm trying to understand 三国演义, I'll post my questions in the process here, please help me answer.

Question 1:
"汉朝自高祖": doesn't this basically mean "The very first Han emperor"? Why is there a "自“ here? What does it mean in this phrase?

Question 2:
"后来光武中兴"
Why is there a "光" in this sentence? I suppose this sentence means "enhances military afterwards", what does “光” do here?

Full context: "汉朝自高祖斩白蛇而起义,一统天下,后来光武中兴". 

[lips]

自 here means "from" (the beginning).

光武 is the title of an emperor. 光武中兴 refers to the "renaissance under 光武", a prosperous period under his reign.