Visions

Visions
Due to the Darkspawn taint Grey Wardens are linked to the 'hive mind' of the Darkspawn. This enables them to 'hear' the Archdemon's commands to the horde. These take form as 'visions' that the Warden's see in their dreams. These visions allow the Wardens to truly know when a Darkspawn attack is truly a Blight. The visions eventually become what is known as The Calling at which point Wardens go to the deep roads to die in battle before they are overcome by the taint.

In-game

 * After the battle at Ostagar, at this point Alistair explains the reason behind them.
 * At a mid-point in the playthrough, in this vision The Archdemon 'senses' both The Warden and Alistair. This is followed by an ambush by Shrieks and if The Warden is a Dalish Elf the appearance of Tamlen