Definitions from [Free Dictionary][1], [Dictionary.com][2], and [Oxford dictionary (subscriber only)][3] should tell you the official definition.  

The Roman Republic and Byzantine Empire are different because of religion, geographical location, population, language and customs.  Although the Byzantine did consider themselves the heirs of the Roman Empire.  In the same way that the Holy Roman Empire is not the same as the Roman Empire in religion, location, language, population, and customs but again a lineage was claimed.  


  [1]: http://www.thefreedictionary.com/civilization
  [2]: http://dictionary.reference.com/browse/civilization
  [3]: http://english.oxforddictionaries.com/definition/civilization