in the Middle Ages
The development of the harness for horses and oxen cushioned the load they pulled and allowed them to pull twice as hard as before.
Water Wheels and Mills
The Romans had occasionally used water wheels and even mills, but the Europeans brought this to a higher art, damming the streams of Europe.
The Three-Crop Rotation System
An important agricultural development, attributed to Charlemagne, was the institution of the three-crop rotation scheme. Prior to 800 A. D., peasants would leave half their fields fallow and would plant the other half. The three-crop rotation scheme left one-third of the fields fallow, planted another third in leguminous crops such as peas or beans, and then planted the remaining third with conventional crops. Not only did this increase the usable land from one-half to two-thirds but in addition, the legumes fertilized the soil, rendering the land more productive. This innovation translated directly into a higher population density.
The Heavy Moldboard Plow
Another crucial innovation was the heavy moldboard plow, appearing around 1000 A. D. The heavy plow was able to turn the dense clay of northern Europe, opening new land to cultivation.
Linen, and the Foot-Powered Loom
The 12th century saw the invention of a loom with foot pedals which enabled weavers to create cloth more quickly and inexpensively. Conventional weavers opposed the new loom, which they recognized as a threat to their labor market. The subsequent invention of the spinning wheel, which made thread faster than before, led to skyrocketing in the production of cloth. The speed of production led to increased popularity of linen. Sheep farmers rioted because the cloth that was being made was not wool.
The linen cloth wore out quickly, but was so cheap that people simply threw it away as casually as we do paper towels. Piles of discarded linen were used to make rag paper, in turn causing the price of paper to drop precipitously. More riots ensued, again by the sheep farmers, because linen paper supplanted sheepskin parchment.
Paper Reaches the European Market
Paper was introduced into Europe from Moorish Spain around 1250. Italy became the major European paper-producing country. This occurred at the beginning of the Renaissance, when Genghis Khan's conquest of China and of Islam opened the floodgates to East-West trade. (This was the century when Marco Polo visited Cathay, and brought East and West together.)
Increased availability of paper led to increased demand for scribes, especially in the wake of the radical population reduction during the Black Death. Scribes went on strike for higher wages, driving up costs. In 1450, Johann Gutenberg eliminated the debate by creating the printing press, which the Church fought because it would encourage free thinking.
Gunpowder Reaches the European Market
This was the era of the Crusades, when Europe became familiar with the then-higher Islamic culture, and developed an appetite for Chinese imports. There is some indication that the Muslim world had harnessed gunpowder for use in warfare as early as, possibly, the 11th century. The first documented manufacture of cannon and bullets in Europe was in 1326, and was directed by the Council of Florence, although there are earlier, debatable references to it as far back as 1284. After that, guns and gunpowder enter the armamentaria of both Christian and Muslim military entourages.
Mechanical Clocks Appear
In the period between 1300 and 1350, the first mechanical clocks began to appear in Italian cities, although it would be another 300 years before Christian Huyghens invented the pendulum clock.
Michael Crichton, in his novel "Timeline", has the 14th-century French water-wheel at Castelgard driving a set of "robotic" hammers for working iron.