At the left is an early 18th century design for a smoke house showing the levels at which certain meats should be hung for optimum effect.
Of course, this relatively complex building is a little bit over the top for most homes or farms. This type of design was for producing mass quantities of smoked meat in as short a time as possible. Most smoked meats go in for 2 to 4 days. A high-level producer would set the goal of 3 rotations per week with one day for cleaning.
The reality is that Barbecue was first mentioned in reference to smoking pigs sometime in the 1880's. The term has been used by restaurants more than anywhere, and the real origin is lost to antiquity.