A century is a period of 100 years. It is commonly used to measure time in history, allowing us to categorize events and developments. For example, the 20th century refers to the years from 1901 to 2000. Centuries help historians and researchers understand the progression of societies and cultures over time. Each century can be divided into decades, which are ten-year periods. The first century began in the year 1 AD and ended in the year 100 AD. Notable events, such as the rise of the Roman Empire or the Industrial Revolution, are often studied within the context of specific centuries to highlight their significance.