What is the role of the MAAM of Grosseto for visiting Roselle?

The MAAM is mainly useful for understanding what you will see later at Roselle : it preserves and displays objects found during excavations, with a section that follows the history of the city, from the first settlements in Roman times to later phases. It is neither the entrance to the archaeological site nor an on-site visitor center: the museum is located in the center of Grosseto, while the ruins are about 10 to 15 km au nord.

If archaeology interests you, visiting the MAAM before Roselle helps put the remains in context; after the walk, it lets you see up close objects that are no longer on the site. But it is not essential for exploring Roselle: on site, you visit the remains themselves, notably the ramparts, the forum and the amphitheater. So plan for two separate visits and a trip between Grosseto and Roselle; don't count on the MAAM to replace the explanations of a guide or an on-site information panel. In short, the MAAM complements the visit to Roselle, it does not determine it.