Layers.

Each one of them is an entity with a beginning and an end
As a whole they are a living form
In constant motion

Past, present and future
Old, new and unknown
Layers of paint
Of walls
Of people
Of buildings
Of vegetation
Layers of earth and rock

Abandoned houses leaning heavily
Across the living walls of new buildings.

Seen this way, layers are the essence of urban evolution.
Cells of an organism reproducing, growing, constantly and continuously changing.