From Migration to Kingdom – Sources and recommended reading.

References:

History of the Later RomanEmpire by J.B. Bury. (e-book).

the LaterRoman Empire by A.H.M. Jones

Armies, War and Society in theWest (ca. 300 – 600 AD) by Richard Abels.

History of the Goths by Herwig Wolfram.

Timeline:

Fectio, Timeline 301 – 400 AD

Fectio, Timeline 401 – 500 AD

Economy

Taxes in the Roman Empire

Roman Economy

The Oxford Roman EconomyProject

Taxation in the Late RomanEmpire, J.A. (Sander) Boek.

General Reading

Books on the Later RomanEmpire (118 titles).

Late Roman Towns in Britain,Rethinking Change and Decline. (e-book).

Digital Map of the RomanEmpire

Currently Reading
Rome's Gothic Wars by Michael Kulikowski
Patricians and Emperors by Ian Hughes

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The campaign rules which have been recently featured here demonstrating three brief campaigns, can be downloaded from the DBA Wiki. - Quick Play Campaigns - Ancient