The gateway dividing the Lower Ark from the Mid-Safe hall of Entry hall 910 was a stone-built marvel of the Second Epoch. A huge portal sixty arm-lengths high and twenty arm-lengths wide, framed by massive stone jambs of dense green coarse grey rock, anchored three hundred feet into the living bedrock of the mountain spine. The coarse grey rock was so dense that steel chisels turned their edges upon it without making a scratch. It had been dressed by the high-pressure abrasives of the First Dynastic Engineers to a mirror-like finish that resisted both acid and salt water. Overhead hung the Great Granite Portcullis. A single, unbroken monolith of grey stone twelve feet thick and seventy feet tall, weighing one hundred and forty thousand pounds, suspended on four massive cables of braided star-fallen iron as thick as an oak tree’s trunk.
Beneath the gate, the doorstep was a deep trough of hammered lead, two feet wide and six inches deep, designed to receive the bevelled lower edge of the drop-gate. When the stone dropped into that bed of soft metal, the huge impact would cold-weld the lead around the granite tongue, forming a hermetic barrier that no volume of water could penetrate.
