The blood was noticed by a horrified employee at the new ticket office, located in the square in front of the Colosseum early on Wednesday morning.
Health authorities were called to deal with the problem.
“A rodent had died in the ceiling cavity and blood was falling onto the desk,” Franceso Prosperetti, archaeological superintendent of Rome told Il Fatto Quotidiano.
The closure created more negative publicity for Rome, as it affected one of the city's most high-profile areas, which is visited by thousands of tourists each day.
Prosperetti denied that the city's most famous archaeological sites risked being overrun by rodents. “There is no rat infestation or invasion at the Colosseum or the Roman Forum,” he said.
He did add, however, that rodents were “a well-known problem that have been causing workers to protest for some time” at the National Roman Museum in Palazzo Massimo – another popular tourist attraction in the city centre.
Prosperetti blamed the rat infestation at Palazzo Massimo on public roadworks taking place in front of the museum.
“It's not down to the archaeological superintendency to tackle the problem,” he added, challenging the city's authorities to tackle the issue which has been getting steadily worse since the start of the year.
Experts say there are now six million rats in the city, meaning there are more than two rats for each of the city's 2.6 million inhabitants.
Rome's rat issue is thought to be exacerbated by refuse collection problems, which often cause rubbish to pile up, even around the Eternal City's most popular tourist attractions.
Some 600 disinfestations were carried out around the city between mid-January and mid-February.
Amid the clamour following the closure, potential candidates for mayor of Rome at the upcoming elections were quick to pipe up over the need to address the city's long-standing rodent problem.
Mayoral nominee for the Five Star Movement party, Virginia Raggi, blasted the city over the news, saying it was “the sign of intolerable degradation."
"We need to change it together and put an end to this shame.”