In what year were the bill of rights added to the constitution as the first 10 amendments?

1791

Explanation:

The idea was originally proposed by the congress in 1789 in order to guarantees of personal freedoms and rights. But the process of changing the amendments tend to be complicated because it need the ratification of the legislatures from at least 3/4 of the States. After passing through all the backlash and criticism, they eventually manage add it on December 15th, 1791.