An unknown attacker gagged and bound the hands of the 57-year-old in the Villa Borghese park north of the centre, according to police sources cited by news agency Ansa.
A taxi driver found the woman at around 1am on Monday morning. He freed her and called the police, who were working in the park for several hours on Monday in search of any evidence which could help track down the perpetrator.
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The woman is a German citizen who has been in Italy for six months but does not have a fixed abode, Italian state broadcaster Rai reported. She was treated for shock at Rome's Santo Spirito, and said her attacker also stole €40 from her.
The incident comes after three reports of rape or attempted in the capital over a two-week period, including a Finnish tourist who was raped close to the Termini train station last week.
Earlier in September, four people were arrested over two gang rapes in the seaside town of Rimini, and the following week two police officers were placed under investigation for the alleged rape of two US students.
Hundreds of women demonstrated in Florence over the weekend to show solidarity with the American students, following Italian media coverage which organizers said reflected "a sexist rape culture [...] that constantly insinuates that the victims ‘were asking for it’".
Cameras, lights, and taxis to tackle violence
"Violence against women, again. The umpteenth monstrous, despicable, and unacceptable act that must not go unpunished," said Rome mayor Virginia Raggi.
The president of the wider Lazio region, Nicola Zingaretti, echoed her words, saying the incident "should not leave us speechless". "First of all, ensure justice; together we raise our voices against violence against women," he wrote on Twitter.
Raggi said that the city administration was "already at work" to clamp down on gendered violence.
Writing in an editorial for Rome-based daily Il Messaggero on Friday, the mayor said: "Recent events across Italy show the need to always keep one's guard up and, above all, to strengthen prevention [in tackling violence]."
She said that the city was working closely with police and public institutions to not only ensure high levels of security, but also to create a "culture of respect" towards women. The city currently has over 4,000 video surveillance cameras in place, many of which are observed directly by police, and Raggi said she had set aside €500,000 to install a further 150, with further plans to improve lighting across the capital at night.
Other policies already in place to ensure the safety of women include a 'pink tariff' on taxis which offers women a discount if travelling at night, a measure which aims to dissuade them from walking home through potentially dangerous areas.
In addition, Raggi said her administration was working with schools, companies, and advertising firms to tackle sexism more generally, with initiatives including sanctions for discriminatory or sexist advertising and the introduction of an anti-violence programme in participating schools to raise awareness.
"It's a topic which is very close to my heart as Mayor, but even more so as a woman," wrote Raggi, who also said that a seat is always kept empty in the room where the council meets, as a tribute to women who have lost their lives to gendered violence.