Encyclopedia Brittanica- Serapeum (ancient temples, Egypt) http://www.britannica.com/EBchecked/topic/523962/Serapeum

This online article consists of a brief overview of the histories of the Serapeum at Saqqara and Alexandria. It also describes the excavations of the former in during the 1850s and the 1980s and the destruction of the latter at the hands of Theophilus, the patriarch of Alexandria.

Encylopaedia Romana- The Destruction of the Temple of Serapis http://penelope.uchicago.edu/~grout/encyclopaedia_romana/greece/paganism/serapeum.html 

This source focuses solely on the destruction of the Serapeum at Alexandria at the hands of the Christians in AD 391. It also includes quotations from prominent intellectuals from Late Antiquity who commented either on the Serapeum’s architectural features or on its fall.