Zaun is the original city, Piltover was built way way way later. Grey is the product of Zaun's mining, progress and technology. Zaun basically destroyed itself later in it's history and sunk beneath the ground. Later it was rebuilt and progress continued, transport was regulated by Zaun and they became extremely wealthy, and as it continued topside of Zaun started disconnecting itself from the bottom and eventually became Piltover. What Cait was watching, was basically Kiraman family fighting for Zaun's right to clean air and construction of the ventilation system, and ofc control over it, so with one press of a button Kirmanas could relase Grey back in the lanes. Before ventilation, Spirit God Janna(also LoL champion) removed the gas from the lanes.
JB
2024-12-03 10:41:30 +0000 UTC
It's not a matter of Piltover "allowing" the grey to move around the lanes. It's based on physics, as the grey is fissure gas (since the underground areas are OG stripmines back when Piltover was being built by the settlers etc, and as anyone can tell, mining releases fucktons of toxic gases etc at the scale the lanes clearly are implying), ergo it by definition ONLY exists underground where mining etc is being done on industrial scale etc