Complex sentence: The Altar of the Twelve Gods (or Sanctuary of the Twelve Gods), was an altar at Athens, Located in the Agora and situated near the Temple of Ares, it was an important point from which distances were reckoned inside the city.
Split into simpler sentences: The Altar of the Twelve Gods (or Sanctuary of the Twelve Gods), was an altar at Athens, located in the Agora near the Temple of Ares. It was an important point from which distances were reckoned inside the city.