The square building is surrounded by a series of concentric walls
and pavements with an eastern facing entrance.
Both craters have bull's-eye structures, with a pair of concentric walls
separating inner and outer sections of the crater floor.
Arata Isozaki and Yoko Ono collaborated on a labyrinth, which she calls a 'penal colony', comprising four concentric walls
of greenish ice blocks, stepping down from 10m to 2.5m in height at the centre.
The die design is reported to boost productivity because tooling can run fixed-center or adjustable-center with concentric walls
at all speeds; the heating system is designed to ensure consistent heat throughout the crosshead; and consistent heat results in balanced polymer flow, thereby providing a stable and concentric finished product.
By the 1340s, Caffa was again a thriving city, heavily fortified within two concentric walls
. The inner wall enclosed 6,000 houses, the outer 11,000.