What causes Beowulf to halt and call the dragon out to fight him?

Beowulf halts his stride in remembrance of all the battles gone before, and then he calls out to the dragon in fury.

Then he saw by the wall who a great many battles

Had lived through, most worthy, when foot-troops collided,

Stone-arches standing, stout-hearted champion,

Saw a brook from the barrow bubbling out thenceward:

The flood of the fountain was fuming with war-flame:  

Not nigh to the hoard, for season the briefest

Could he brave, without burning, the abyss that was yawning,

The drake was so fiery. The prince of the Weders  

Caused then that words came from his bosom,  

So fierce was his fury; the firm-hearted shouted:  

His battle-clear voice came in resounding

’Neath the gray-colored stone. Stirred was his hatred,

Beowulf calls out under the stone arches.

The hoard-ward distinguished the speech of a man;