Starling flocks on the Roman roosts of the Campagna follow topological, not metric, neighbours — each bird copies about seven others. Here a metric radius is a close, cheap analogue. Polarisation Φ = |⟨v̂⟩| is 1 when every bird points the same way and 0 when the cloud is a scramble. A hawk injects a repulsive potential; the fold and split you see is the same “wave of agitation” measured in real murmurations.