Citadel

The Citadel is a skyscraper in the city of Insomnia in the Final Fantasy XV Universe where the royal family live, and where the Crystal of Lucis is kept in the center. The light of the Crystal emanates from the Citadel and into the sky to project the Wall that protects Insomnia, upheld by King Regis.

Outside the Citadel
The gates to the Citadel are heavily guarded. When Emperor Aldercapt and his convoy arrive for the treaty-signing ceremony, their vehicles pull to the outside of the Citadel. There is a in the middle of this area.

Painting of the prophecy
A large room within the Citadel has numerous paintings that depict the coming of the True King. The one-winged Oracle gives her blessing to the King of Light who emanates light that is making the hordes of daemons below shun away. The True King is accompanied by three companions. The old kings of Lucis and the astrals stand watch. Seven swords face the daemons from the king. Neither Ifrit or Ardyn are depicted on the paintings.

When the player visits this room in Final Fantasy XV, Noctis remarks he didn't like it as a child, as his father was always so sombre in there. When the player visits the room, they can look at the pictures along the walls. Staying in the room and looking at the paintings has the party make various comments, including Gladiolus wondering whether the story they depict will come true with Noctis affirming he will make sure of it, Ignis commenting that when Noctis was young he had left a mark in a painting and had his attendant cover it, and the party noting how Ardyn—the darkness of legends—doesn't appear in any of the paintings.

Throne room
The room has two sets of stairs leading to the golden throne that is surrounded by elaborate metalwork.

Crystal chamber
The Crystal whose light emanates into the sky from this room is kept in the Crystal chamber in the middle of the building between the four "towers." The room is sealed by a vault.

Crownsguard training room
The Citadel has training areas for the Crownsguard. It can be visited in the Tutorial for Final Fantasy XV and it is glimpsed at in Brotherhood Final Fantasy XV.

Story
The Wall that protects Insomnia, and thus the Crystal, is projected from the Citadel at the behest of the reigning monarch via the Ring of the Lucii, a royal heirloom said to originate from the gods of Eos. The kings of Lucis are sworn to protect the magical Crystal until the prophesied time when the True King would be born of their lineage. Paintings depicting the coming of the True King are kept in a prominent room in the Citadel. Upholding the Wall drains the monarch's life-force, and Regis has aged beyond his years and become frail, and thus when Chancellor Ardyn Izunia arrives to offer terms of peace, he feels out of options.

The Citadel is where the royal family lives, but to gain independence Prince Noctis has an apartment in the city where he stays most of the time, although he still has a room at the Citadel as well. As depicted in Final Fantasy XV Prologue Parting Ways Noctis heads to the Citadel with Ignis Scientia the day before he is to depart to Altissia for his wedding. Noctis is to see his father, King Regis, but is told the king is too busy. While at the Citadel he bumps into Iris Amicitia who is at the Citadel to see her father, Clarus Amicitia, King Regis's bodyguard who is in a meeting with the king. She has brought a change of clothes for her father who's been so busy lately with the preparations for the peace treaty between the kingdom of Lucis and the empire of Niflheim, he sleeps at the Citadel.

Noctis and Ignis head to Noctis's quarters. Noctis doesn't know if he will still use his room at the Citadel after the wedding, as Luna, his bride, would live with him. Noctis and Ignis reminisce of the times they snuck out of the Citadel together. Noctis had hated being stuck in the Citadel as he couldn't get a moment alone, though he knows it is because everyone worried about him after his childhood incident.

At the Crownsguard's training hall, Clarus Amicitia tells Gladiolus, his son, about the security measures in place during the signing ceremony and Prompto Argentum arrives for his Crownsguard uniform he is to wear for his trip with Noctis. In the Kingsglaive briefing room, Drautos asks arranges for Nyx Ulric to drop Noctis off to his place as the Kingsglaive will be using Noctis's car to ferry important guests for the treaty-signing.

Noctis spends his last night in Insomnia at his apartment in the city, and the next day they return to the Citadel. They meet King Regis at the throne room who sends them off to their journey. As the descend the steps outside the Citadel, Regis catches up with Noctis for a final farewell. After Noctis leaves Insomnia, everyone prepares for the upcoming peace treaty signing ceremony. Emperor Aldercapt arrives with Chancellor Ardyn Izunia and Princess Lunafreya Nox Fleuret, Noctis's bride, although Regis had sent a Kingsglaive member to escort her to Altissia for the wedding. Regis is relieved to meet Luna at the throne room nonetheless, seeing that she holds no grudge against him or Lucis, unlike her brother Ravus.

The Kingsglaive soldier Nyx Ulric becomes Luna's bodyguard, and when she is held hostage outside Insomnia Ulric mobilizes the Kingsglaive to save her. During the rescue operation he discovers many Kingsglaive members have turned on the king, and that the operation was a distraction. While the Kingsglaive are away, the Empire attacks Lucis, steals the Crystal from the Citadel, and the Wall dissipates allowing the Empire to deploy its magitek infantry and daemons into the city.

Nyx and Luna make their way back to Regis at the Citadel, and Regis gives Luna the Ring of the Lucii so she can hand it to Noctis. Nyx, Luna and Regis begin to escape the Citadel together, but in the room of the paintings of the prophecy Regis erects a magic barrier between himself and the two, asking them to go without him. Regis is killed by General Glauca of Niflheim, while Nyx and Luna make their way out. Nyx gains the power of the old kings to fight the Empire and Glauca and stays behind, and Luna escapes Insomnia and begins her journey to rendezvous with Noctis.

The Citadel is the only lit building in the ruins of Insomnia ten years later when Noctis returns to fulfill his destiny as the King of Light. Insomnia is abandoned for all but the daemons and Magitek Troopers left behind from the invasion ten years ago. The world has been taken over by the Starscourge and is engulfed in an endless night. Noctis meets Ardyn outside the Citadel, who ushers the astral Ifrit upon him. Noctis fells Ifrit with the help of the other astrals, and makes his way to the Citadel. In the room of the paintings Noctis asks to see the photos Prompto took during their journey, and takes one of them with him to face Ardyn at the throne room.

Ardyn sits upon the throne. He is Noctis's immortal ancestor who has become the embodiment of the Starscourge that plagues the world, and he has brought the Crystal back to Insomnia in wait for the True King. Noctis fights Ardyn and fells him outside the Citadel. He sends his friends away in the same manner his father sent them on their journey ten years ago, and then returns to the throne room to offer his life to fulfill the prophecy. He sits upon the throne and calls upon the spirits of the old kings, who attack him until Noctis dies and his soul enters the Ring of the Lucii. Noctis and the combined powers of the Lucian monarchs destroy Ardyn's spirit in the afterlife. The Ring of the Lucii disintegrates and the sun rises upon the world.

Noctis and Lunafreya appear together at the Lucian throne marked Noctis Lucis Caelum CXIV in wedding attire, while Regis Lucis Caelum gives them his blessing.

What becomes of the Citadel and the rest of Insomnia afterward is unknown, as there are no heirs to the throne.

Creation and development
The Citadel appears to be designed after the real-life. It first appeared in the Final Fantasy Versus XIII E3 2006 trailer where Noctis descended the stairs outside to alone face a line of armored soldiers.

Platinum Demo – Final Fantasy XV
Outside the Citadel is the final area of the demo where Noctis fights an Iron Giant. The area is shown at day-time, unlike in the final game. The player can point-warp up the building.