Giving your search a context will help you do a better one. Sources such as these will help you focus on the who-what-when-where of your question, and provide suggestions for where to go to find the why.
First choice for new and experienced scholars, this updated edition remains essential as a starting point for research in ancient Greek and Roman cultures. Contains solid definitions and biographies of people, places, things, and cultural ideas from Greece and Rome. Also good for mythological genealogy. With references to primary and secondary sources.
The Lexicon Iconographicum Mythologiae Classicae (abbreviated LIMC) is a multivolume encyclopedia cataloguing representations of mythology. Published serially from 1981 to 2009 it is the most extensive resource of its kind. Entries are arranged alphabetically, with black-and-white illustrations indexed to their respective entries.
A comprehensive encyclopedia of antiquity, with solid coverage of topics famous and obscure. Need a biography of Pseudo-Skimnos? This is the place. We also have a comprehensive collection of prior editions in the Pauly series.
A collection of modern scholarly essays on topics and time periods in antiquity. Not as good for narrative as the first edition, but very comprehensive bibliographies.