Q: Context: The ability to block a measure through extended debate was an inadvertent side effect of an 1806 rule change, and was infrequently used during much of the 19th and 20th centuries. In 1970, the Senate adopted a "two-track" procedure to prevent filibusters from stopping all other Senate business. The minority then felt politically safer in threatening filibusters more regularly, which became normalized over time to the point that 60 votes are now required to end debate on nearly every controversial legislative item. As a result, the modern "filibuster" rarely manifests as an extended floor debate. Instead, "the contemporary Senate has morphed into a 60-vote institution -- the new normal for approving measures or matters -- a fundamental transformation from earlier years." This effective supermajority requirement has had very significant policy and political impacts on Congress and the other branches of government.

Question: when did the filibuster start in the us senate?
Let's give stream of consciousness below
The relevant sentence in the passage is: The ability to block a measure through extended debate was an inadvertent side effect of an 1806 rule change, and was infrequently used during much of the 19th and 20th centuries. So the answer is 1806.