Piccinin said on Monday they faced "real violence" and mock executions after being captured by rebel forces in April.
Quirico, 62, is a well-known war correspondent in Italy who worked from African hot spots including Libya, Sudan, Darfur and Mali. He entered Syria from Lebanon without an official visa and went missing in early April between Damascus and the flashpoint central city of Homs.
Scant detail has emerged of their release on Sunday but Quirico's newspaper said Italy's secret services had stepped up efforts to secure their release ahead of feared US military strikes.
"Physically, we are okay despite the torture we suffered," Piccinin told Bel RTL radio station shortly after returning to Belgium.
"There was sometimes real violence …humiliation, bullying, mock executions … Domenico faced two mock executions, with a revolver," he said.
Piccinin, a history teacher in a southern Belgian town, and Quericio, a correspondent for Italy's La Stampa daily, entered Syria via Lebanon in April.
Shortly afterwards, the Western-backed Free Syrian Army picked them up and handed them over to the Abu Ammar brigade, a rebel group "more bandit than Islamist," Piccinin told Le Soir daily.
The five months they were held proved to be "a terrifying odyssey across Syria," he told Bel RTL.
"We were moved around a lot…it was not always the same group that held us, there were very violent groups, very anti-West and some anti-Christian."
Piccinin said they tried to escape twice, once while their captors were at prayer, but they were tracked down after two days and "seriously punished."
Piccinin, an Arabic speaker who has travelled to Syria seven times since the conflict broke out in 2011, said the rebel cause had changed, descending into banditry.
"I think it has become very dangerous for Westerners to go to Syria in current conditions, with the revolution (against President Bashar al-Assad) disintegrating," he said.
After the two men were freed Sunday, they were flown to Rome on an Italian government plane.
Quirico, who was on his fourth trip to Syria when he was kidnapped, spoke to prosecutors in Rome on Monday about his ordeal after meeting with Prime Minister Enrico Letta.
Quirico looked gaunt and tired in images shown on Italian television.
"I have lived for five months as if I was on Mars. I was badly treated and scared," he told journalists.
La Stampa said the kidnappers were part of the "galaxy of rebel groups – a jumble of slogans, movements and war profiteers that is hard to work out."
The concern had been that as the possibility of US-led air strikes on Syria increases, "the frontline could move rapidly and contact could be lost with kidnappers," it said.
During his captivity, Quirico was able to briefly call his wife on June 6th, apparently from the former rebel bastion of Qusayr, near the Lebanese border, southwest of Homs.
The foreign ministry later called on the media not to published unconfirmed information about the kidnapping and to let caution prevail when reporting about the case.
Italy is also trying to free another one of its nationals missing in Syria since July, Father Paolo Dall'Oglio, a Jesuit priest who has lived in Syria for many years to promote inter-religious dialogue.
Following Quirico's release there are 13 journalists still missing in Syria, according to media rights watchdog Reporters Sans Frontieres (RSF).
Among the kidnapped are two French journalists, Didier Francois and Edouard Elias, who were picked up in June on the road to Aleppo. According to the head of their support committee, Serge July, they are being held by a group that claims to be part of the resistance.
US journalist James Foley, 39, who worked for Global Post, Agence France-Presse and other international media, was kidnapped in northwest Syria and has been missing since November 22nd 2012.
Foley's family have said they believe he is being held by Syrian security services in a detention centre near Damascus. In an interview in May, Syrian President Bashar al-Assad said he had "no information" on this.