Century/ˈsentʃəri/ Definition 1 of 3Pro Tip 1/3Historical Eras Centuries categorize history into 100-year blocks to simplify reference to specific eras. The Renaissance spanned the 14th to the 17th century. Pro Tip 2/3Ordinal Numbers When talking about centuries, use ordinal numbers like 20th, 21st to describe sequential order. The telephone was invented in the 19th century. Pro Tip 3/3Common Misunderstanding The 20th century refers to the years 1900-1999, not 2000-2099, as might be commonly misunderstood. World War II happened in the 20th century.