Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Remaining Signs of Past Centuries (Arabic: Kit b al- th r al-b qiyyah ''an al-qur n al-kh liyyah, also known as Chronology of Ancient Nations or Vestiges of the Past, after the translation published by Eduard Sachau in 1879) by Ab Rayh n al-B r n is a comparative study of calendars of different cultures and civilizations, interlaced with mathematical, astronomical, and historical information, exploring the customs and religions of different peoples. Completed in AD 1000 (AH 390/1), it is the first major work of Al-Biruni''s, compiled in Gorgan, at the court of Qabus, when he was in his late twenties.