Operation Rhalgr's Beacon is a joint operation by the Ala Mhigan Resistance and Eorzean Alliance late in the plot of Final Fantasy XIV: Stormblood, aimed at liberating the Garlean territory of Ala Mhigo and its vicinity, Gyr Abania. The operation occurs in the aftermath of the battles of Baelsar's Wall and the summoning of Shinryu, causing open war between the Alliance and the Empire. Thanks in part to the aid of the recently-liberated nation of Doma, the XIIth Legion is defeated militarily and driven out of Gyr Abania, while a strike team lead by the Warrior of Light breaks through the defenses of the Ala Mhigan Royal Palace itself, killing the tyrannical Legatus Zenos yae Galvus and Shinryu, which he had seized for his own use. After the fighting ceases, Ala Mhigo declares independence.
The XIIth Legion's response to the occupation of Baelsar's Wall by the Alliance is to send a force personally lead by Zenos to attack Rhalgr's Reach. The Resistance suffers heavy casualties in the battle, and the many wounded are withdrawn to Castrum Oriens, leaving Rhalgr's Reach poorly defended. As a result, the Alliance is forced to call off its planned attack on Castellum Velodyna and send the Scions of the Seventh Dawn to Doma to seek out allies. This mission is a success, as the Empire loses all of its holdings in Yanxia, most notably Doma itself, in the battle of Doma Castle. Furthermore, Lord Hien Rijin of Doma sends couriers throughout the Empire to spread word of the fall of Yanxia and incite rebellion in other Garlean territories.
With the Empire destabilized and on the verge of its second civil war in a year, Flame General Raubahn Aldynn decides that the time has come to launch a joint attack on Castellum Velodyna, thus liberating the Fringes. His name for the plot, Rhalgr's Beacon, refers to the plan by which he means to take the Castellum.
During the Scion's mission to Doma, Krile Mayer Baldesion, who had remained behind in Gyr Abania, is captured by the Garlean army for use in human experimentation.
Fall of the Fringes
Flame General Aldynn leads a massive Alliance host out of Castrum Oriens and into the no-man's-land of the western Fringes. The leader of the Skulls, Fordola rem Lupis, orders a Garlean army out to meet them—a tactical error, as this allows a small Resistance force under Lyse Hext to occupy the western bridge outside of the Castellum and send M'naago Rahz to glamour the Garlean flags over the Castellum to look like Ala Mhigan flags, making it seem that the Castellum had fallen. Though Fordola herself leads a team to stop the Resistance squadron from providing cover fire, M'naago's mission is a success, causing mass panic in the Garlean host, whose generals now believe it to be sandwiched between Aldynn's army in the west and an unknown force which has seized Velodyna. The Garlean army routs, suffering massive casualties, and is only able to regroup east of the Velodyna River, near Djanan Khat, where, after killing several Ananta (and causing them to summon the primal Lakshmi, which must be struck down by the Warriors of Light), they withdraw to Specula Imperiatoris in the Peaks.
Zenos, who is already frustrated with the loss of Doma, is furious at the fall of the Fringes, and orders Fordola to submit to human experimentation as punishment. Based on their prior experimentation with the Echo-blessed Krile, this leads to the creation of a prototypical Resonant: a human without natural magical abilities, who nonetheless has access to the Echo and can manipulate aether. Zenos orders Fordola to lead the front lines from Castrum Abania, the next Imperial fortress after Specula Imperiatoris. Because Specula Imperiatoris and Castrum Abania are both at chokepoints in the road through the Peaks, the Resistance force would have to take both fortresses before advancing into the Lochs and ultimately to Ala Mhigo itself.
After occupying the Fringes, Aldynn's force marches east into the Peaks, where the garrison of Ala Ghiri surrenders without a fight, and, along with the Resistance force under Conrad Kemp, lays siege to Specula Imperiatoris.
Catastrophe at Specula Imperiatoris
At the first opportunity, the Alliance-Resistance force breaks into Specula Imperiatoris, with men under Aldynn and Vice Marshal Pipin Tarupin fighting to take the ground floors while Kemp's host seizes the towers, which are defended by the Ala Mhigan collaborators known as the Skulls. Unwilling to fight their countrymen, the Skulls surrender to Kemp.
At Zenos's counsel, Fordola gives the order for the ceruleum cannons of Castrum Abania to fire upon Specula Imperiatoris, destroying the structure and crushing thousands of Garlean and Eorzean forces alike, including the Skulls that were once under her command. Among the dead is Kemp; from this point onward, Lyse becomes the leader of the Resistance. Fortunately for both sides, Estinien Wyrmblood sneaks into the Castrum and destroys a ceruleum pipeline, forcing the slaughter to end.
However, though the Eorzean forces are badly defeated at Specula Imperiatoris, they are still able to occupy the ruins of the fortress, and begin planning for an attack on the Castrum itself. However, the castrum is atop Mount Yorn and it is not known that the ceruleum cannon is still defunct, so before regrouping and continuing their march eastward, the Alliance sends the Scions of the Seventh Dawn to the nearby town of Radiata to investigate the Castrum. Though several residents of Radiata attack the Scions out of fear of an Imperial reprisal, after meeting with a spy by the name of Stark Woad the Scions are able to find a path inside Castrum Abania: through the ventilation ducts.
Two squadrons—one consisting of the Leveilleur twins and another of the Warriors of Light, sneak inside the Castrum and cause a distraction by attacking the weapons research laboratory, allowing men under Lyse to break into Castrum Abania and attack the cannon bay, which is defended by Fordola and her troops. With the aid of Resonance, Fordola is able to badly injure Alisaie Leveilleur before fleeing; with the cannons under Eorzean control, the Alliance launches a full-on assault on the Castrum. Because their magitek weapons have been destroyed by the Scions' mission, the Garlean force is once again routed, surrendering the Peaks and regrouping in Ala Mhigo proper.
Despite the heavy casualties incurred by the Alliance, the campaign for Mount Yorn proves even more catastrophic for the Garleans: their provisions are lost to Eorzean looting, providing the rebel forces with the resources to march on the Lochs.
Battle of Ala Mhigo
Once the Peaks have been secured, the Eorzean troops gather at Porta Praetoria, an encampment west of Loch Seld. On the advise of an Ala Ghannan named Wiscar, the Scions seize a key from Sali Monastery which unlocks a tunnel into the Ala Mhigan Quarter. Through this, Lyse is able to swim through Loch Seld and through open an Ala Mhigan gate, allowing the Scions to attack in the city, capturing Fordola by way of an anti-Resonance device invented by Urianger Augurelt, and rescuing Krile. In the confusion, the Alliance forces march east. Their Ul'dahn thaumaturges and Lominsan cannons begin firing on the main gates of the city, only to meet the Garlean aerial magitek armor. However, the Doman army, flying on yols obtained by their alliance with the Xaela of the Azim Steppe, arrive and defeat the Garlean air force. Upon learning that Doma has fallen, the Farae Domitae, who are Doman conscripts to Garlemald, turn on the Garlean army, clearing a path for the Eorzean army to enter the city.
The last of the XIIth Legion makes a desperate stand against the Alliance within the city, but despite fierce urban combat, the Warriors of Light are able to enter the Royal Palace of Ala Mhigo, destroying waves after waves of magitek armor and trained dogs. Near the Royal Menagerie, the Warriors face Zenos yae Galvus, who has been empowered with Resonance and the katana he looted from the Kojin of the Red. As the city falls to the Alliance, Zenos fuses with Shinryu, who he had kept bound in the Menagerie through the whole war, and battles the Warriors of Light. Though Shinryu, through the power of the Eyes of Nidhogg, is able to unleash aether sufficient to create a protostar, as well as utilize all of the ultimate attacks of several primals, the Warriors are able to prevail. With the death of Shinryu, Zenos commits suicide, and what is left of Legion surrenders. As the Eorzean army withdraws from the Royal Palace, Estinien is finally able to complete his life's mission: by destroying the Eyes of Nidhogg, he is able to end the hateful legacy of the Dragonsong War. Ala Mhigo declares independence.