But another brigade came up to their relief and they advanced again, sending a heavy return fire from their rifles, while the artillery on their flank replied to that of the South.
The combat now became fierce.

The Invincibles in the very thick of it advanced to the water's edge, and fired as fast as they could load and reload.

Huge volumes of smoke gathered over both sides of Bull Run, and men fell fast.

There was also a rain of twigs and boughs as the bullets and shells cut them through, and the dense, heated air, shot through with smoke, burned the throats of blue and gray.
But the South had the advantage of position and numbers.

Moreover, those riflemen on the flanks of the Northern troops burned them terribly and they were weary, too, with long marching in dust and heat.
As the artillery and rifle fire converged upon them and became heavier and heavier they were forced to give way.