London

It went on its way, flying into the haze of smoke above the Rustwater Marshes, where artillery duels were rumbling like autumn storms. A squadron of enormous Traction Cities was crawling eastward, trying to head off a Green Storm counterattack. On their lower tiers, whole buildings had been converted into snout guns. Railways carried huge high-explosive shells out of the cities' innards, and the guns hurled them into the marshy Out-Country ahead, which was said to be crawling with Stalkers and mobile rocket units. Buffeted by
passing airships and the fluffy white thistledown of antiaircraft bursts, the gull let the leading city's slipstream carry it eastward for a while, then rose above the battle and flapped on toward the white mountains that stood on the rim of the world.

Infernal devices pg 135/237, Chapter 21: The Flight of a Seagull