The Pyramid Builders were a mysterious civilisation that existed centuries before the events of the Mortal Engines Quartet. They built pyramids up in the high Ice Wastes for unknown reasons.

They were described to be "so far North you started going south again." Inside the mysterious pyramids were the Remembering Machines; stalker-like machines that remembered the past.

After Anna Fang had been killed by Thaddeus Valentine, the Green Storm took a stalker brain from the pyramids before blowing it up, perhaps to prevent the traction cities from developing their own models.

This particular culture had extremely advanced technology, contending with or perhaps on level with that of the Sixty Minute War. They existed during the Black Centuries when the smoke from the war blotted out the sun and 'plague storms' periodically destroyed large numbers of people.

It is not known exactly when they existed, but they died out a long time before even the early Traction Era.