United States History Student Edition

given unique names to represent that specific period. These longer blocks of time are called eras or ages. For example, the thousands of years when people lived by hunting and gathering food and made stone tools is called the Paleolithic Era. Historians also divide human life on Earth into four very long periods. The first of these is called prehistory. Prehistory refers to the time before people developed writing, about 5,500 years ago. This is followed by the period known as ancient history, which ended in c. 500 C.E. (c., or circa, means “about”). Historians call the next thousand years the Middle Ages. After that, modern history begins and continues to the present day. Calendars A calendar is a system for breaking time into units. It allows us to measure how much time has passed between events. Cultures throughout the

world have developed different calendars based on important events in their history. The calendar we use has a year made up of 12 months and 365 days, which are organized into 7-day periods called weeks. Some cultures base their calendars on the cycle of the moon. The Chinese and Jewish calendars, for example, base their months on the appearance of the new moon. Dating Events Each year is given a number, which allows us to identify events that happened in one year and those that happened in another. The dates in this program are based on the Western calendar. The Western calendar was originally Christian and begins with the year in which Jesus was thought to have been born. The years before the birth of Jesus are known as B.C.E. (“before common era”). The years after are called C.E. (“common era”). Some people also use B.C., or “before Christ,” and A.D., or annno domini , which is Latin for “in the year of the Lord.”

era a historical period

This illustration from a late 1400s manuscript shows the 260-day religious calendar of the Aztec, who had an empire in what is now Mexico. The Aztec also had a 365-day agricultural calendar.

DEA Picture Library/De Agostini/Getty Images

Historian’s Toolkit HT9