Accordingly the Romans straightway set fire to the tree-trunks which had been prepared for this purpose.  But when the fire had burned only a certain portion of the embankment, and had not yet been able to penetrate through the whole mass, the wood was already entirely exhausted.  But they kept throwing fresh wood into the pit, not slackening their efforts for a moment.  And when the fire was already active throughout the whole embankment, some smoke appeared at night rising from every part of the hill, and the Romans, who were not yet willing to let the Persians know what was being done, resorted to the following device:  They filled small pots with coals and fire and threw these and also ignited arrows in great numbers to all parts of the embankment.  And the Persians who were keeping guard there, began to go about in great haste and extinguish these, and they supposed that the smoke arose from them.  But since the trouble increased, the barbarians rushed up to help in great numbers, and the Romans, shooting them from the wall, killed many.  And Chosroes too came there about sunrise, followed by the greater part of the army, and, upon mounting the hill, he first perceived what the trouble was.  For he disclosed the fact that the cause of the smoke was underneath, not in the missiles which the enemy were hurling, and he ordered the whole army to come to the rescue with all speed.  And the Romans, taking courage, began to insult them, while the barbarians were at work, some throwing on earth, and others water, where the smoke appeared, hoping thus to get the better of the trouble; however, they were absolutely unable to accomplish anything.  For where the earth was thrown on, the smoke, as was natural, was checked at that place, but not long afterwards it rose from another place, since the fire compelled it to force its way out wherever it could.  And where the water fell most plentifully it only succeeded in making the bitumen and the sulphur much more active, and caused them to exert their full force upon the wood near by; and it constantly drove the fire forward, since the water could not penetrate inside the embankment in a quantity at all sufficient to extinguish the flame by its abundance.  And in the late afternoon the smoke became so great in volume that it was visible to the inhabitants of Carrhae and to some others who dwelt far beyond them.  And since a great number of Persians and of Romans had gone up on top of the embankment, a fight took place and a hand-to-hand struggle to drive each other off, and the Romans were victorious.  Then even the flames rose and appeared clearly above the embankment, and the Persians abandoned this undertaking.