The equations between Greek and Roman gods are essentially translations - Mars is the Latin for Ares in the same way that arbor is the Latin for dendron. When Romans wanted to refer to Greek stories of the gods, but in Latin, they would use the Latin translations. As a result, it looks to many people as if the same stories existed about Roman gods as about Greek gods; in reality it's an artefact of translating into Latin.

Here's a couple of my posts from earlier this year that touch on aspects of this topic:

• native homegrown Roman gods and how they got 'syncretised' with Greek ones
• methodological problems with the word 'syncretism', in the context of Herodotus referring to 'Osiris' as 'Dionysus'