First, in the middle ages, castles were made to protect the population of the town or village they surrounded. Later they were used as a defence for the lord, and a show of power in the feudal system. Need more info?/ use http://www.middle-ages.org.uk/development-of-castles-in-the-middle-ages.htm
Castles in the early middle ages were motte and bailey castles- a motte was a large mound and a bailey was like a courtyard. These developed into the standard castle with strong stone walls etc.
The middle class developed in Northern society in the early 1800s.
Islam (the religion of Muslims) Started in Saudi Arabia (Middle East) in the Early 7th century.
Transcendentalism was the religious and philosophical movement in the U.S. in the early to middle-1800's. It developed in the 1820's and was a protest against the state of spirituality.
Kidwelly Castle was built in the early 13th century.
There were many languages that developed in the Early Middle Ages. Old English was one. Old High German was another. Old Saxon developed, and would eventually become Low German. The medieval Latin called Vulgar Latin developed, and would lager continue doing so to produce the later medieval and modern Romance Languages, including French, Spanish, Italian, Portuguese, Romanian, and so on. Old Welsh and Old Irish both developed in the Middle Ages.
allegra's castle (an early 90's children's show)
Castle MacLachlan, Scotland
in the early 13th century
Leonardo DaVinci.
Yes, polyphony was used during the Middle Ages. We do not have any real idea of when polyphony was introduced, but the earliest texts describing it date to the Early Middle Ages. By the end of the Middle Ages, it was highly developed. There is a link below to an article on polyphony, beginning at the section on its origins.
If this helps, It stood from the early 13th century to the early 18th century.