Old Valyria

Valyria was a once-great empire spanning much of the continent of Essos. At its height it encompassed most of the eastern continent and reached as far as the current Free Cities and the island of Dragonstone off the coast of Westeros. The Targaryens were of Valyrian origin and continued to practise several Valyrian customs in Westeros.

In the books
In the Song of Ice and Fire novels, this empire began its rise to power over five thousand years ago when the people of the small city of Valyria found dragons lairing in the nearby volcanoes. Finding a way of binding the dragons to their will, the Lords Freeholder of Valyria overran the neighbouring empire of Ghis, throwing it down in defeat five times before annexing it fully. Eventually Valyria stretched for thousands of miles along the coasts of Essos and far inland, expanding into the far western coastal regions where it overran the lands watered by the River Rhoyne (displacing the native Rhoynar people to Westeros, where they settled in Dorne) and annexed or established eight powerful colony-states. Refugees from these states founded the city of Braavos as a secret refuge from the Valyrians. The Valyrians also established a stronghold on the island of Dragonstone, settling the Targaryens there, possibly to faciliate trade with the then-independent Seven Kingdoms.

Valyria was utterly destroyed in a cataclysmic event known as the Doom approximately four centuries ago. This event obliterated the Valyrian Peninsula, leaving it a storm-wracked land surrounded by boiling seas emitting poisonous fumes, wiped out almost every dragon in the western world (bar only the dragons of the Targaryens on Dragonstone) and also saw the disappearance of magic from all the lands to the west of Valyria. In the aftermath of the Doom the eight colony-states threw off their Valyrian overlords and became the Free Cities, eventually joining one another in trade and commerce links, along with the Secret City of Braavos to the far north. The Targaryens survived and launched a devastating invasion of Westeros almost three centuries ago, eventually uniting the entire continent under their control.

The Valyrians had a number of different gods, which the Targaryens abandoned for the worship of the Seven instead. They also had several customs that the Targaryens continued to practice, including the idea of marrying brother to sister and being able to have more than one wife at a time.

Another key remnant of the time of Valyria are artifacts, particularly weapons made of Valyrian steel. Weapons of Valyrian steel are incredibly sharp, never need maintenence and have unusual dark colours flowing along the blade. There are over 200 such weapons in Westeros, mostly serving as family heirlooms, such as the Stark greatsword, Ice.