What was that

"What was that?" asked Graham.
"'I am awakened and my heart is with you.' And bow--bow royally. But first we must get you black robes--for black is your colour. Do you mind? And then they will disperse to their homes."
Graham hesitated. "I am in your hands," he said.
Ostrog was clearly of that opinion. He thought for a moment, turned to the curtain and called brief directions to some unseen attendants. Almost immediately a black robe, the very fellow of the black robe Graham had worn in the theatre, was brought. And as he threw it about his shoulders there came from the room without the shrilling of a high-pitched bell. Ostrog turned in interrogation to the attendant, then suddenly seemed to change his mind, pulled the curtain aside and disappeared.
For a moment Graham stood with the deferential attendant listening to Ostrog's retreating steps. There was a sound of quick question and answer and of men running. The curtain was snatched back and Ostrog reappeared, his massive face glowing with excitement. He crossed the room in a stride, clicked the room into darkness, gripped Grahams arm and pointed to the mirror.
"Even as we turned away," he said.
Graham saw his index finger, black and colossal, above the mirrored Council House. For a moment he did not understand. And then he perceived that the flagstaff that had carried the white banner was bare.
"Do you mean--?" he began.
"The Council has surrendered. Its rule is at an end for evermore."
"Look!" and Ostrog pointed to a coil of black that crept in little jerks up the vacant flagstaff, unfolding as it rose.
The oval picture paled as Lincoln pulled the curtain aside and entered.
"They are clamourous," he said.
Ostrog kept his grip of Graham's arm.
"We have raised the people," he said. "We have given them arms. For today at least their wishes must be law."
Lincoln held the Curtain open for Graham and Ostrog to pass through.
On his way to the markets Graham had a transitory glance of a long narrow white-walled room in which men in the universal blue canvas were carrying covered things like biers, and about which men in medical purple hurried to and fro. From this room came groans and wailing. He had an impression of an empty blood-stained couch, of men on other couches, bandaged and blood-stained. It was just a glimpse from a railed footway and then a buttress hid the place and they were going on towards the markets.
The roar of the multitude was near now: it leapt to thunder. And, arresting his attention, a fluttering of black banners, the waving of blue canvas and brown rags, and the swarming vastness of the theatre near the public markets came into view down a long passage. The picture opened out. He perceived they were entering the great theatre of his first appearance, the great theatre he had last seen as a chequer-work of glare and blackness in his flight from the red police. This time he entered it along a gallery at a level high above the stage. The place was now brilliantly lit again. He sought the gangway up which he had fled, but he could not tell it from among its dozens of fellows; nor could he see anything of the smashed seats, deflated cushions, and such like traces of the fight because of the density of the people. Except the stage the whole place was closely packed. Looking down the effect was a vast area of stippled pink, each dot a still upturned face regarding him. At his appearance with Ostrog the cheering died away, the singing died away, a common interest stilled and unified the disorder. It seemed as though every individual of those myriads was watching him.