History of Waterdeep - Age I, The Rise of the Warlords:

Over the years, the forest was cut back farther and farther from the shore, and tribes began to stay most of the year there, farming the cleared land. The wiser among them claimed and controlled some of the timber in order to trade for more weaponry and tools. Such claims angered many who found the squatters rich from frequent trade, and brought attacks from land and sea, the more warlike tribes slaughtering the more sedentary settlers. Noted among these tribes was that led by Nimoar, a chieftain who ordered his people to seize the farms, crude wooden docks, trading sheds, and storage barns built up around the bay. They settled there themselves, and erected a log palisade within an earthen embankment to protect the holdings. After several abortive pirate and tribal raids, Nimoar's people thrived in their new home, a fledgling town referred to as "the town of Water-deep."

Farther north, orc tribes had outgrown their mountain strongholds. Attempts to expand underground met with fierce dwarven resistance (although many small gnomish colonies were overwhelmed and wiped out), and the orcs spread out on the surface of the land, coming south and down out of the mountains, hurling their seemingly endless numbers against all who stood in their path. Here and there elven enclaves held out, but the push southward displaced many other northern inhabitants, including the "everlasting ones" (trolls), who came down into the newly-cleared lands northeast of Nimoar's Hold, those lands now known as the Trollmoors. Nimoar died of old age during this time of increasing danger. Younger War Lords led the men of Waterdeep (for so the ship-captains called the harbor) in battles against the trolls. There were many bloody struggles between men and trolls for a decade, until the magic of a Northem youth named Ahghairon turned the fortunes of war against the trolls, and the "everlasting ones" were destroyed or scattered. Ahghairon rose slowly in skill and power with the passage of years, until he became a great mage. He discovered a supply of potions of longevity (or learned the art of making such), for he lived on, still physically a man in his prime, for decade upon decade.

Fearing further attacks, the men of Waterdeep raised a small keep on the slopes of Mount Waterdeep above their farms, where fire arrows from on high could defend against attacking trolls. Many outlying tribes who had come to the settlement for safety from the trolls stayed, and expanded the walls with new farms several times. War Lords ruled the Free City of Waterdeep, holding it independent and increasingly wealthy as years passed.