Dendrochronology

Cybertron is very crowded.

When a new spark is born, it is placed into a specially-forged protoform. Although Cybertron is a world made entirely of metal, not just any metal will do - protoforms must be made of the "living metal" from which all Cybertronian life is formed. As the spark grows, so too must the protoform grow to accommodate it. As the protoform grows, so too does the amount of energy required to power it.

A Transformer can live forever, but their spark will never stop growing. At each new stage of their life, they must visit the blacksmiths, who nurture their growth by adding new layers of living metal. The most drastic change occurs when it is time for a Transformer to choose their alternate form - a complicated process steeped in tradition, by the end of which their body will have doubled in size.

The oldest Transformers fell still millennia ago, and their titanic frames form the cities in which their descendants now live. To keep the cities alive, new suburbs must constantly be added - all constructed entirely from living metal.

Long ago, as the borders of the cities met, they expanded in the only direction available: up. Vast quantities of living metal were moulded into towering skyscrapers, piled endlessly atop one another, reaching - grasping - at the stars, at life. Their voices became naught but the low wind that whistled between the spires.

Cybertronians do not bury their dead. They bury their living.

The youngest Transformers do not know where living metal comes from. They live in the newest dwellings, above the thick layer of smog which obscures the lower levels. It is no great secret. If they so wished, they could see the source for themselves - were they willing to spend the years needed to venture down the endless stairwells and navigate their way through the arterial catacombs along which fuel yet flows. Along the way, they could count the layers for themselves, and witness the lifetime of their species. At the end of their journey, in the strangled air of Cybertron's wilderness, they would find the trees, and witness how little remains of that lifetime.