The medieval period, or the Middle Ages, covers about 1,000 years from the fall of the Roman Empire to the start of the Renaissance. The Roman Empire fell in 476 and the Renaissance began in the 1400s after the Black Death wiped out a third of Europe's population.
The medieval era is often divided into three sub-periods: the Early Middle Ages, the High Middle Ages and the Late Middle Ages. The first period starts with the fall of the Roman Empire and lasts until about 1000 CE. Often, this period is still called the Dark Ages mainly because we know very little about it compared to antiquity or later periods. One marking event for the end of the Early Middle Ages is the Peace and Truce of God in 989.
After this came the High Middle Ages, which contained most of the trappings people think of being associated with the medieval period, such as the birth of universities, the era of chivalric romance, the Crusades and the rise of elaborate castles. It lasted until about 1300, with the foundation of the Ottoman Empire and the return of Marco Polo to Italy. This sparked European interest in Asia.
Finally, the Late Middle Ages lasted from 1300 until the start of the Renaissance. It saw the rebirth of art and science, a focus on humanism and the rise of the merchant class.