The Poros detention site started operating as an informal screening facility in 2011 in a former military outpost – commonly referred as fylakio [φυλάκιο] in Greek – whose management was transferred to the Greek Police. The exact date of the transfer is unclear. The refurbishment of the building and equipment for its operation were co-financed by the EU External Borders Fund programme (75%) and the Greek government (25%). It formally started operating on 5th March 2012, and was referred to as a ‘Centre for the First Management of Illegal Immigrants’ between 2012 and 2015.

The facility functioned as a screening centre for individuals apprehended within the jurisdiction of the Alexandroupoli Police Directorate in the region of Evros. Its primary purpose was to facilitate reception and identification procedures as part of Greece's national migration and asylum plan aimed at addressing shortcomings in the country's border management and asylum systems. Greek police officers, alongside Frontex staff specialising in screening and debriefing, conducted these procedures. There are few official sources to evidence the function of the centre between late 2015 and 2020. Other sources nevertheless suggest that it continued to be a screening facility. Following that period, the Hellenic Police described the facility as a temporary detention centre where people crossing from Turkey were held before their transfer to the Fylakio Reception and Identification centre or Border Guard Departments in the area. In April 2021, the Hellenic Police told Amnesty International that the facility was not operational at the time. However, Frontex internal documents inadvertently revealed that 78 of the 92 men that were found, according to the Greek authorities, naked at the Greek-Turkish border on 15th October 2022 were temporarily detained in Poros.

The 2020 CPT report describes the detention space as a ‘large, unfurnished room’ on the left of the P-shaped building. According to a testimony given to Amnesty International, families were detained on the right wing of the building, and single people on the left. Information on conditions of detention at the Poros facility is generally limited. With the exception of a monitoring visit of the CPT in 2020, no other Greek, European or international body has inspected the Poros facility since 2016. The most recent visual depictions of the facility consist of a photograph published by the CPT and videos filmed by a researcher in 2019.