Primary sources:
Livy:
The very best source for 4th century BC (and a generally crucial source for Roman history all throughout, i.e. the Etruscans). In books 6-10 he covers all of the important events such as the the Samnite Wars (books VIII-X); invasion of Alexander of Epirus (book VIII, 3, 17, 24); and other important events:
- link (Perseus Project On-Line),
- link (B. J. Butterfield's Ancient History site),
- Books 1-5, 6-10, 21-25, 26-32, 33-39, 40-45 (Virginia University E-Text Library)
Dionysius of Halicarnassus:
Detailed information about early Roman history and such people as the Etruscans (called by Greeks the Tyrrhenians):
- link (Lacus Curtius).
Appian:
- The Samnite Wars (www.livius.org)
Strabo:
- Geography (Lacus Curtius) of:
Latium and Samnium,
Tyrrhenia and Umbria,
Northern Italy,
Cisalpine Gaul,
Picenum and Campania (Part II),
Sicily,
Iapygia (Southern Italy).
Justinus:
- Book XII, 2 of Epitomes for Alexander I of Epirus and his invasion of Italy (www.forumromanum.org)
Plutarch:
- Life of Pyrrhus of Epirus (Lacus Curtius)
- Life of Pyrrhus of Epirus (MIT Internet Classics Archive)
Aulus Gellius:
- Book XVII, 21 of Noctes Atticae, on Alexander I of Epirus (cached Google page)
More primary sources will be added later, along with articles from archeological and scholarly publications.