Eusebius at the Christian Broadcasting Works: [the wonky link, be warned]
 http://web.cbn.org/bibleresources/theology/eusebius/churchhistory/index.asp

Eusebius at Newadvent.org:
 http://www.newadvent.org/fathers/

Eusebius at Christian Classics Ethereal Library [CCEL]:
 http://www.ccel.org/fathers2/NPNF2-01/TOC.htm

Just for fun, the Edict of Milan, Constantine and Galerius, AD 311:
 http://www.fordham.edu/halsall/source/edict-milan.html

More fun, The Internet Encyclopedia of Philosophy, s.v. Origen [AD 182-251]:
 http://www.utm.edu/research/iep/o/origen.htm

Ditto, the Christian Catacombs of Rome:
 http://www.catacombe.roma.it/welcome.html

For something a bit different, have a look at the summary of Ross Kramer, Her Share of the Blessings: Women's Religions Among the Pagans, Jews, and Christians in the Greco-Roman World Oxford University Press (1992):
 http://www.pinn.net/~sunshine/book-sum/blessing.html