The studio made the announcement via the game's website. Beginning on Friday, players levels 5 to 60 can take part in an assault of the Tower District to take down the Many-Arrows orcs. According to the post, Call to Arms events are modified versions of the different skirmish zones. Players can queue for the event any time it's active.
"Parties who successfully complete a Call to Arms Event may be rewarded with companions, dye packs, transmutation items (items which change the appearance of your equipment) and other unique rewards," the post reads."These rewards will vary and will be unique to each adventure zone's Call to Arms Event."