First, I have some slight refinements of what I posted yesterday (I swear I'm not trying to copy how +Ryan M. Danks posted his adventure fractal, I'm really not).
The completion of an arc achieves an arc milestone. This is basically a minor milestone in line with what Fate Core recommends. The campaign overall will have a campaign milestone - this is a major milestone, and typically results in changing a campaign aspect or affecting some other campaign-scale change. Arcs and campaigns are each their own level in the fractal. Typically, the arc milestones will be part of the campaign milestone's stress track. There also may be side events that can achieve the campaign milestone that aren't part of any arc - in fact, they might be absolutely necessary in order to achieve it. If you are anticipating using Consequences to soak milestone stress, you probably should have at least 15 stress worth of events that can be dealt or at least be prepared for some of them to be ad hoc.
The arc should have a set of skills that can be used to create milestone-level advantages, set passive resistance or defend against actions the PCs take that would cause milestone stress, and maybe even perform attack actions. Ideally, these would actually be campaign skills that capture the theme of the entire campaign. I'm thinking that whatever roll the PCs made which triggered the event would be used as the roll the milestone defends against. For example, if the PCs complete a Challenge to build a fortified wall across the major bridge leading, the most relevant roll (probably Crafts) would be used to attack the milestone stress track and the appropriate campaign skill would be used to defend. The stress listed for the event would serve as a floor for the stress inflicted.
Milestone Fractal Example
I'd use Children of Lilith for this example but I don't want to give anything away, so I'm going to take a stab at a simple campaign for my rudimentary Dixton campaign setting. The campaign involves deposing the Governor of the city and breaking the gentry's hold on the torchpod plantations - pretty big stuff. The PCs are all assumed to all be unsavory types - smugglers, thieves, fences, etc. - but still relatively prominent among their peers. The campaign starts in The Piles, which is your typical sort of wretched hive of scum and villainy ala Flea Bottom from A Song of Ice and Fire or The Maze from Thieves World. I'm just going to set the campaign milestone and the first arc milestone for this example; I'm also not going to define any locations, NPCs, or any of the other details that would likely be needed.
Heroes Emerge From The Most Unlikely Sources
The Governor Must Be Stopped (issue)
The Governor has recently discovered that the Piles rests on the ruins of a major Sia complex, which contains technology that, if he controls it, could result in both a near monopoly on torchpod production and allow him to greatly expand the city's territory in the peninsula. It's just that there are a bunch of thieves, pirates, smugglers, and - purely by happenstance - innocent but poor people in the way. Of course, no one will complain too much if they get relocated to somewhere a bit less inconvenient and the whole place razed to the ground, right?
Stress: 3 boxes, three consequence slots (mild, moderate, severe)
- Completing Arc 1: 1 stress
- Completing Arc 2: 2 stress
- Completing Arc 3: 3 stress
- Killing the Governor: 2 stress
- Disrupting torchpod production: 1 stress
- Enlisting the aid of the Sia: 2 stress
Note that the non-arc actions can potentially be combined, so enlisting the aid of the Sia to disrupt torchpod production would be 3 stress. The arcs intentionally step up the stress to show their importance to reaching the campaign milestone - the assumption is consequences would only be used to absorb campaign stress if the players really come out of left field.
Arc Aspect: Bridge Over Troubled Waters
The Governor starts his purge of The Piles, citing the general lawlessness and threat to the health of the city. This starts as sending in more police (who don't normally enter the district at all) and then regular army troops, instituting curfews, cracking down on criminal syndicates, etc. The PCs need to stop him, if only to save their own skins (and livelihoods).
Stress: 3 boxes, three consequence slots (mild, moderate, severe)
- Discovering the reason for the Governor's plan: 1 stress
- Preserving one of the PCs "operations": 1 stress
- Short term disruption of police activities: 1 stress
- Rallying the residents of the Piles to resist "involuntary relocation": 2 stress
- Completely disrupting or stopping police activities: 2 stress
- Fortifying or otherwise creating a viable defense against the Governor's forces (such as burning or blowing up bridges, blocking waterways, etc): 2 stress
- Successfully repelling the Governor's forces: 3 stress
- Successfully obtaining control of and/or destroying the Sia complex: 3 stress
As you can see, the events within the arc are designed to allow the PCs to have several means of reaching the arc milestone. What the next arc aspect would be is dependent on exactly how the campaign goes - the second arc might be a full-on assault on the Piles, or the PCs taking the fight into the city proper and trying to rouse the general populace. The third arc might center around a full insurrection against the Governor.
Since the campaign has a pretty solid theme, the skills are relatively easy to define. With some inspiration from The Spark's Mind, Body, Heart and Spark attributes, I think they can be broken down to:
- Control: Used whenever the Governor performs actions regarding controlling The Piles, such as setting up curfews, closing roads, cutting off supplies, etc. Can create milestone level advantages, and defend against the PC's actions which trigger events that would subvert said control.
- Force: Used whenever the Governor brings force against The Piles as a whole, such as large-scale sweeps or attacks against large groups. This can be used to defend against actions the PCs take that trigger actions which would harm or otherwise disrupt police or army units operating in The Piles.
- Intel: Used whenever the Governor is gathering information within The Piles, and can create arc-level advantages. It can also be used to defend against PC actions that trigger events to gather their own intelligence or disrupt the Governor's intel gathering operations.
- Instigation: Used whenever the Governor is trying to sway public opinion one way or the other, or when defending against milestone events that would do the same.
Hopefully this gives an idea of how I see a milestone fractal working - it's definitely helped solidify a couple of things in my head about how to actually set up the stress track.