Given the task definition and input, reply with output. This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Passage: In agriculture, the increased usage of sheep with long-fibred wool allowed a stronger thread to be spun. In addition, the spinning wheel replaced the traditional distaff for spinning wool, tripling production.[AI] A less technological refinement that still greatly affected daily life was the use of buttons as closures for garments, which allowed for better fitting without having to lace clothing on the wearer. Windmills were refined with the creation of the tower mill, allowing the upper part of the windmill to be spun around to face the direction from which the wind was blowing. The blast furnace appeared around 1350 in Sweden, increasing the quantity of iron produced and improving its quality. The first patent law in 1447 in Venice protected the rights of inventors to their inventions. Question: What new type of windmill was invented in this period?
the tower mill