Omashu

Omashu was the second largest city in the Earth Kingdom and the capital of one of its provinces. It is located in the Kolau Mountain Range in the southwestern Earth Kingdom surrounded on all sides by steep canyons and an enormous gorge. The cities' three gates are composed from massive stone, each five feet thick and towering over thirty feet high. As a result they are accessible only by skilled Earthbenders who guard its only entrance. Omashu's has developed a complex and efficient mail system used to transport goods throughout the city that employed Earthbending and gravity using extensive ramps and chutes.