History is all in the past, it may be just a day, decades, and even centuries . History is similar to a puzzle, once a piece is gone, we may or may not be able to recover it. However, there is historical evidence that may help us fill in that missing puzzle piece . A few years ago on September 11th, 2001, a tragedy shook the United States as one. The twin towers collapsed in downtown Manhattan. It was a heartbreaking story. Due to this event, our country has strengthened security.Examples of primary sources in this situation is a personal interview from a person who witnessed the collapse or a recording of the tragic moment . Secondary sources include textbooks that report on 9/11.  Sources, whether they are secondary or primary still help us digest the knowledge that happened over the course of thousands of years.