The Middle Ages cover about 1,000 years--from about AD 500 to about AD 1500. The change from ancient ways to medieval customs came so gradually, however, that it is difficult to tell exactly when the Middle Ages began. Some historians say that the Middle Ages began in AD 476, when the barbarian Odoacer overthrew the emperor Romulus Augustulus, ending the Western Roman Empire. Other historians give the year 410, when Alaric, king of the Visigoths, sacked Rome. Still others say about AD 500 or even later. It is equally hard to determine exactly when the Middle Ages ended, for decisive events leading to the modern age took place at different times. Historians say variously that the Middle Ages ended with the fall of Constantinople, in 1453; with the discovery of America, in 1492; or with the beginning of the Reformation, in 1517.