"Although western-European society in the Middle Ages developed no general concept of progress, many important innovations were made. ...[M]edieval inventions included... spectacles for reading, the spinning wheel, stronger iron tools... the heavy ... es. Some of the most important innovations in the Middle Ages were connected with the use of the horse... A more efficient harness than the crude yoke, which had been so well suited for draft-oxen, was introduced about the ninth century. ...Alfred the Great noted, with apparent surprise, that horses were used for ploughing in Norway. This would have been impossible with the yoke-harness, because as soon as the horse begins to pull with it the neck-strap presses on the animal's windpipe and thus tends not only to restrict the flow of blood... but also to suffocate it! ...Previously, the horseshoe] had only been tied on... The first indisputable evidence of the use of nailed horseshoes goes back to the ninth century. ...[M]etal armour ...gave considerable impetus to the craft of the blacksmith. ...[T]he blacksmith was the forerunner of those who constructed the first mechanical clock. ...[T]he greatest of these, ...in the early fourteenth century ...was the son of a blacksmith."