Christians in the Iraqi city of Mosul are openly celebrating their first Christmas in four years following the liberation of their city from the clutches of ISIS, AFP has reported. Mass opened with the singing of the Iraqi national anthem as worshipers filed in, while armored cars and police watched outside to protect the safety of worshipers from any remaining extremists in the city.

The city of Mosul once had one of the larger Christian populations in the Middle East, but the ongoing warfare in Iraq had caused many Christians to flee by the time ISIS occupied the city in 2014. AFP estimates that around 2,000 Christian families remained in Mosul at that time.

When ISIS invaded, they prohibited public Christian worship services and began systematically destroying Christian churches. Almost all of Mosul's Christian population was either killed or fled the city to escape ISIS' purges.

However, Iraqi security forces mounted a bloody and ultimately successful campaign to retake the city which ended in July of this year. Some estimates place the number of civilian casualties at over 10,000 during the battle.

AFP estimates that since the battle ended, around 70 or 80 Christian families have returned to Mosul, and more are expected to do so in the coming weeks and months if Iraqi security forces are able to succesfully demonstrate that they can protect the city from being retaken by ISIS or other extremist groups.

The successful liberation of Mosul and other ISIS strongholds has been touted as a major foreign policy success by the administration of President Donald Trump. In addition to aiding Iraqi forces during the liberation of Mosul, U.S.-led forces have driven ISIS from their stronghold Syrian city of Raqqa.

The Iraqi government formally declared victory over ISIS earlier this month, noting that while ISIS remains a threat to launch guerilla attacks in the country, they no longer control any meaningful territory in the country. At the height of their power, it was estimated that ISIS controlled as much as one-third of the country of Iraq, as well as significant portions of Syria.