What did the three-field system involve?

The three-field system involved planting three different crops in a seasonal rotation, which was a significant advancement in agricultural practices during the medieval period in Europe. This system allowed for more efficient use of land and improved food production by ensuring that not all fields would be left fallow at the same time. Typically, one field would be planted in the autumn with grains (like wheat or rye), another field would be planted in the spring with crops such as oats or barley, and the third field would remain fallow to recover its nutrients. This rotation not only prevented soil depletion but also helped to increase yields, which contributed to population growth and the development of towns and trade during the period.

In contrast, using only one type of crop each season (the first choice) would limit agricultural diversity and could deplete soil nutrients, while leaving all fields fallow every year (the third choice) would not promote the higher productivity that the three-field system achieved. Farming on mountains and hills only (the fourth choice) is unrelated to the three-field system, as this agricultural practice was implemented primarily in flat and arable land areas throughout much of Europe.