EUSEBIUS Pamphilus who wrote in the 4th century
http://www.ccel.org/fathers2/NPNF2-01/TOC.htm
http://www.ucalgary.ca/~vandersp/Courses/texts/eusebius/eusehe.html
ZOSIMUS, who wrote in the 4th century
"The New History" Books 1-6 @
http://www.earlychristianwritings.com/fathers/index.htm
SULPITIUS Severus, who wrote in the 5th century
"Life of Saint Martin"
http://www.ccel.org/fathers2/NPNF2-11/Npnf2-11-05.htm
"The Virtues of Martin"
http://www.ccel.org/fathers2/NPNF2-11/Npnf2-11-13.htm
"The Sacred History"
http://www.ccel.org/fathers2/NPNF2-11/Npnf2-11-22.htm
Hermias SOZOMEN, who wrote in the 5th century
http://www.ccel.org/fathers2/NPNF2-02/TOC.htm
"The Ecclesiatical History"
http://www.ccel.org/fathers2/NPNF2-02/Npnf2-02-18.htm
SOCRATES Scholasticus, who wrote in the 5th century
http://www.ccel.org/fathers2/NPNF2-02/TOC.htm
"The Ecclesiastical History"
http://www.ccel.org/fathers2/NPNF2-02/Npnf2-02-05.htm
PROCOPIUS of Ceasaria who wrote in the 6th century
"The Secret History"
http://www.fordham.edu/halsall/basis/procop-anec.html
Procopius of Caesarea (TOC 4 works)
http://procopius.net/contents.html
EVAGRIUS, who wrote in the 6th century
Ecclesiastical History 431-594
http://www.tertullian.org/fathers/evagrius_0_intro.htm
Ecclesiastical History
http://www.earlychristianwritings.com/fathers/evagrius_0_toc.htm
MAMALAS, who wrote in the 6th century
JOHN OF EPHESUS, who wrote in the 6th century
Ecclesiastical History, Part 3 http://www.earlychristianwritings.com/fathers/ephesus_0_toc.htm
The Venerable BEDE who wrote in the 7th century
"Ecclesiastical History of England"
http://www.forham.edu/halsail/basis/bede-book1.html
"Conversion of England"
http://www.forham.edu/halsail/source/bede1.html
"Gregory the Great"
http://www.forham.edu/halsail/source/bede-greggrea.html
Along with these primary sources, I will quote the writings of what are called 'the fathers' of the church and the actual texts of Church Councils.
A list of these councils, the fathers and their writings, along with many excellent secondary sources such as Gibbon's Decline of the Roman Empire are compiled at
http://community.webtv.net/tales_of_the_western_world/RLSOURCES