A Humble Military Outpost
For the first century of its existence, Volantis was little more than a military outpost established to protect the borders of the Valyrian empire, with no inhabitants save the soldiers of its garrison.
From time to time dragonlords descended to take refreshment or meet with envoys from the Rhoynar cities upriver.
Over time, however, taverns and brothels and stables began to sprout up outside the Black Walls, and merchant ships began to call as well.
^ The funny thing is how Valyria didn’t see at first the vast potential for a giant harbor city where Volantis is located, even though the southern mouth of the Rhoyne screams for such.
They were quite content to leave it as a basic military outpost until a city and giant economic hub naturally sprung forth.
If you build it, they will come… 😉
Growth In Trade & Influence
For much of its early history, Volantis benefited from the trade between Valyria and the Rhoynar, waxing ever more prosperous and powerful … whilst Sarhoy, the ancient and beautiful Rhoynish city that had previously dominated that commerce, suffered a corresponding decline.
Inevitably, this led the two cities into conflict.
(Volantis taking away the economy of Sarhoy)
Though the dragonlords of Valyria won the victory, it is rightly said that Volantis was the principal beneficiary.
Sarhoy remains in ruins to this day, a desolate and haunted place, whilst Volantis, with its Long Bridge and Black Walls and huge harbor, ranks among the great cities of the world.
^ This war was already covered exhaustively in the Rhoynar section.
Even with Sarhoy losing all of its influence and wealth, Valyrian imperialism is what caused the Rhoynish war — not the Rhoynish becoming angry and retaliating over Volantis stealing Sarhoy’s economy — the Rhoynish still had the entire river to themselves.
Valyrians — like Romans, but with dragons.
Daniel's Backup of 20 years of ASOIAF Historical Analysis 