Replicating the authenticity of Rome isn't easy to nail, unless you're talking about HBO's version, where apparently everything is nailed with very little effort. For a Cambridge spot getting the city's food right: L'Impasto.
The first solo bid from the legitimately Roman former chef of North End highlight Ristorante Fiore, L'Impasto (which translates loosely and made-uply as "limp pasta") is an authentic-as-it-gets Italian eatery peddling fresh handmade pastas and breads in a quaint 20-seater that welcomes guests with an open kitchen, an intimate two-table sidewalk patio, and hung kitchenware, which, ladies will love even more than normal kitchenware. Classic noodles include bucatini w/ Italian bacon in a white wine tomato sauce, clams and broccoli rabe tossed w/ olive oil & gnocchetti sardines, and pappardelle covered in a zucchini sauce w/ baby shrimp, also the name of the pop song that has mad crustacean tweens crushing on Bieber. Assuming you already had spaghetti for lunch, they're also slinging pizzas like a prosciutto/ zucchini/ smoked mozzarella white plus noodle-less classics like a balsamic smoked salmon with olives & fennel, and veal scaloppine w/ sage, whose wisdom apparently wasn't enough to keep it from getting eaten.
To round things out, LI hawks to-go breadbaskets overflowing with fresh-baked anchovy loaves and prosciutto-topped focaccia, and for dessert, serves a wild berry tiramisu so decadent, it could be on HB -- oh, god... are they really showing that?