The Remaining Signs of Past Centuries (Arabic: کتاب الآثار الباقية عن القرون الخالية Kitāb al-āthār al-bāqiyah `an al-qurūn al-khāliyah, also known as Chronology of Ancient Nations or Vestiges of the Past, after the translation published by Eduard Sachau in 1879) by Abū Rayhān al-Bīrūnī 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 1000 AD (AH 390/1), it is Al-Biruni's first major work, compiled in Gorgan, at the court of Qabus, when he was in his late twenties. Source: Wikipedia (en)