The great Council developed later into the Lords and the Commons known as a parliament.
这里know as修饰什么？
known as a parliament 是过去分词短语，作定语修饰Commons 。
known as ... 的意思是“作为......而出名的”、“被叫做......的”、“大伙公觉得......的”，也可以作表语。如：She was known as an excellent dancer. 她被大伙公觉得出色的舞蹈演员。（摘自《薄冰英语惯使用方法词典》p.460）