In 2012, the Cohort started to gain power and began a campaign of terror in order to impose fear on the Nephilim society and carry out their plans of restricting Downworlder rights and proceed with the Registry.
Shortly afterwards, Horace Dearborn, the leader of the Cohort, called for all Shadowhunters to return to Alicante to witness his staged parley, as a show of power, with the newly-ascended King Oban of the Unseelie Court, to end the dispute between the two sides and further drive the Downworlders away.
Upon hearing of these news, Julian Blackthorn called a war council against the Cohort, in the Sanctuary of the Los Angeles Institute. He used his influence as the former non-official head of the Institute and contacted Shadowhunters and Downworlders from all factions, with whom he had dealt in the past and that he considered as potential allies.
Many guests showed up and, during the meeting, the Cohort's plans were revealed as well as the truth about Jace and Clary's alleged death, and their stance against the Cohort's rule was discussed. Lastly, Julian explained their plan to interrupt the parley to expose the Cohort's lies and plots to every Shadowhunter watching it and revealed their army banner, disclosing that the resistance was called Livia's Watch, in honor of his sister, Livia, and as a reminder of all the losses suffered because of the Cohort.
After some attendees Portaled to Alicante, a second meeting took place for the reliable allies only, since Julian was counting on having spies of the Cohort present in the first gathering. That was later proved to be true, for the Cohort raised an eidolon demon and had it kill and transform into Oskar Lindquist so it could infiltrate the war council.
In Idris, Livia's Watch divided into teams and while the first group marched to the Imperishable Fields and interrupted the parley, the second group stayed back at the campsite set up in Brocelind Forest and ambushed the Cohort members who were sent to kill Jace and Clary. They later joined the first group and corroborated their story, with Julian also ensuring its authenticity by using the new Mortal Sword.
After the truth was revealed, a battle against the Cohort and the Unseelie faeries broke out and the Shadowhunters and Downworlders from Livia's Watch fought side by side and came out victorious. Upon their defeat, the Cohort was tried for their crimes and when Alec Lightwood, the new Consul, chose to submit to their terms to avoid a tragedy, all the Shadowhunters from Livia's Watch left Idris. The Downworlders had refused to attend the meeting, not wanting to be in the same room as the Cohort.
Livia's Watch had an army-like banner, painted by Julian. The central item of the banner was a saber painted in pale gold, point down, and a locket with a circle of thorns on the front hanging from its hilt, in honor of Livia, whose weapon of choice was the saber and always wore the locket around her neck. Behind the saber spread a pair of angel's wings for Shadowhunters and a cluster of symbols for Downworld – a star for vampires, a moon for werewolves, a spell book for warlocks and a four-leaf clover for faeries.