Primary Sources

[D B Campbell]

I've always assumed a primary source to be one written or produced at the time, usually a document, inscription or artifact but sometimes a literary record, a diary, a collection of letters or a personal account - sort of raw material, undigested and often open to interpretation.
A secondary source would be anything written with historical hindsight, which relies on other (primary) sources for its information.

This is correct. Here are the Oxford English Dictionary entries:
Primary evidence:
[attachment=10592]OED-Primary_source.jpg[/attachment]
Secondary evidence:
[attachment=10593]OED-Secondary_source.jpg[/attachment]

It makes no difference that neither Polybius nor Livy was present at the Battle of Cynoscephalae. If we wish to study the battle, they are our primary evidence. Our critical evaluation of their evidence then becomes a secondary source. (The term "tertiary source" is often used pejoratively to describe those works of synthesis that appear not to have consulted the primary sources, but have relied only on secondary sources.)