All was well, until one day they met a thunderstorm - more than a thunderstorm, a thunder-battle. You know how terrific a really big thunderstorm can be down in the land and in a river-valley; especially at times when two great thunderstorms meet and clash. More terrible still are thunder and lightning in the mountains at night, when storms come up from East and West and make war. The lightning splinters on the peaks, and rocks shiver, and great crashes split the air and go rolling and tumbling into every cave and hollow; and the darkness is filled with overwhelming noise and sudden light. Bilbo had never seen or imagined anything of the kind.