Answer:
Nobody today knows for sure, but the huge unfinished obelisk at a cave at Aswan give us a good idea how such monuments were made. First of all the architects insisted that the stone to be used should have no defects, cracks or blemishes. Next the rock was cleaned and the surface of the rock was scraped until it was smooth and flat. After smoothing, the contours of the obelisk were marked out on the ground and a deep ditch was bashed out of the rock out around them by gangs of slaves hammering away with pounding balls made from dolerite. These were especially hard stones made from dolerite, dark coloured basalt from the desert valleys of Egypt. These stones weighed anything up to 5 kilograms each.
The fourth face of the obelisk was torn from the seam of rock with enormous wooden wedges which were driven into previously prepared holes at regular intervals. The wedges were soaked with water, and as they expanded the rock split.
At this stage hundreds maybe thousands of slaves, depending on the size of the obelisk, worked with ropes and jacks to raise the obelisk from the ditch and to heave it on to planks resting upon a massive sledge. It was a scene of organised chaos as hordes of naked slaves swarmed about the great stone. Although there was no throbbing machinery there was noise: of stone grinding on stone, the creaking of straining timber, the shouts of the foremen and the chanting of slaves. Once it rested safely on its sledge, more slaves dragged the obelisk to the bank of the Nile. Here it was loaded it onto a long barge made from papyrus reeds to be taken to its destination.