The Bryn Mawr Classical Review offers lively reviews of scholarly books published in Classics. This RSS feed highlights the most recent reviews published, but you can go to their website to search for reviews of older books.
In secondary sources, authors analyze and interpret primary source materials.
Secondary sources can be scholarly or popular. Scholarly sources (sometimes called "academic" or "peer-reviewed" sources) are written by and for experts and typically include bibliographies and citations. Popular sources are written for a general, non-expert audience and can be authored by anyone.