The teenager’s funeral was held at the San Valentino church in her hometown of Cisterna di Latina, just south of Rome.
Pink and white balloons were tied to lamp posts and signs throughout the small town, while a banner outside the church read “Justice for Desirée”.
Wreaths were also laid, including one from the Lazio regional government.
Mariottini’s body was found in an abandoned building used as a squat in the Roman district of San Lorenzo on October 19, two days after she called her grandmother to say she’d missed the last bus home and would be staying with a friend for the night.
San Lorenzo is known for its vibrant nightlife and for being a hotspot for drug dealing.
Investigators suspect Mariottini fell unconscious for several hours after being given drugs by several people, and died of an overdose.
She was gang raped before she died.
Two Senegalese men aged 26 and 43, a 40-year-old Nigerian man, and a Gambian man have been arrested.
It is expected the four suspects will be charged with group sexual violence, voluntary manslaughter and drug dealing.