Montrose had only waited to bring up some heavier guns from Dunnottar. On the 17th an advanced party of his troopers encountered an equal number of the Gordon horse within six miles of the town, and were beaten back with the loss of two men. The Gordons were led by the gallant Johnston, who implored Aboyne to let him advance with the whole body of his cavalry. The advice seemed good to all but Gun, and Aboyne, in the face of repeated warnings, still listened to Gun.
Yet the prospect was far from hopeless. The Dee was in flood, and the only approach was by the bridge, a fine structure of seven arches, two miles distant from the city. This had been hastily fortified. The gate at the southern end had been closed and strengthened with turf and earth; the roadway was lined with stout citizens who knew how to handle a musket. Johnston was in command, and the cavalry were gathered on the farther bank, ready to act should the passage be forced. On the morning of the 18th the attack commenced. Montrose had planted his artillery on a hill a few hundred yards south of the bridge, and under a hot cannonade the Covenanters advanced to the assault. But the guns made more noise than execution, and the Aberdonians were no Highland caterans to be frightened by noise. Twice the assailants fought their way on to the bridge-head, and twice they were beaten back by Johnston and his musketeers. Some companies from Dundee, which had ever been jealous of Aberdeen, made a special request to Montrose to be allowed to try their hands. He bade them go on in the name of the Covenant. But so hot was the fire that met them, and so grim looked the ranks of horsemen on the other side, that they wavered and broke before the gate was reached, amid the jeers of the citizens who, like the three Romans on the bridge at Janiculum, bade their rivals welcome to Aberdeen. The spirit of the city rose high. All ranks swore to stand their ground to the last; and women, bringing meat and drink down to their gallant defenders, moved about unshrinking amid the storm of shot and the shouts of the combatants. All day the fight raged, and when the sun fell the Covenanters were forced to own themselves as far from Aberdeen as ever.