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The memorial hallway was created by the crew of Galactica to aid the survivors of humanity to find any loved ones who may have been rescued from the Cylon destruction of the Colonies and were lucky to find themselves on one of the many ships in the battlestar's care.
Five days after the Fleet's escape from Ragnar, Specialist Socinus and other crew are gathering a record of surviving colonists for the new Colonial government, but cannot upload photos to the database (or possibly to other ships) at that moment. When Anastasia Dualla offers her photos to Socinus, he suggests to leave the photo with his group or to place it outside in one of Galactica's hallways. Opting for the latter, Dualla encounters hundreds of photos, newspaper clippings, drawings, and other mementos of loved ones presumed lost or missing in the new Cylon war (TRS: "33").
Despite the Fleet registry's completion, the memorial has remained and is periodically updated and visited by many as a personal shrine. Crewmembers and civilians can often been seen praying there, lighting candles and mourning the dead. With no possibility of visiting their dead in cemetaries, the Memorial Hallway serves as a cenotaph or "Yahrtzeit wall" for Colonials and their newly-mortal Cylon allies alike.
Louanne Katraine adds a picture of Reilly's girlfriend to the hallway in hopes that she will not be forgotten as quickly as the pilot (TRS: "Scar"). Over a year later, Kara Thrace adds Katraine's photo to the wall beneath Katraine's addition, after Katraine succumbs to radiation poisoning (TRS: "The Passage"). Following a promise made by Lee Adama to Kara Thrace prior to her death (TRS: "Maelstrom"), he places a photo of her on the wall, near Katraine's photo (TRS: "The Son Also Rises").
Since joining the fleet, Rebel Cylons have also been witnessed placing images and pictures of fallen comrades on the memorial wall. Most notably on the wall are an image of Natalie Faust, as well as images of two unnamed Eights, a Six and a Two. At least one of the images seems to be a Colonial Identification card. President Roslin and Admiral Adama's discovery of the Cylons' adoption of the practice cements their realization that the two societies' integration is a fait d'accompli irrespective of their own ambivalence (TRS: "Deadlock").
After Adama gives the order to abandon Galactica, most of the pictures in the hallway are taken down except those that were placed there by people who later died during the journey to Earth. Hotdog retrieves the photographs of dead pilots to ensure they will not be forgotten.
In addition to the memorial hallway, the Viper pilots on Galactica have a special picture in their ready room that they touch as they exit as a memorial to other fallen comrades; a copy of the same photograph hangs on the bulkhead of President Roslin's office aboard Colonial One (TRS: "33").