The fort was designed to be surrounded by three concentric layers of walls and its four corners were built into protruding bastions for better defense.

An ooid forms as a series of concentric layers around a nucleus.

These grains are approximately spherical and have concentric layers reaching 10 mm in diameter.

These fields comprised two concentric layers, one excitatory and the other inhibitory.

The European Union is sometimes compared to an onion (as a sphere) with concentric layers.

This rock is filled with nodules of black mica and quartz, in concentric layers.

It has concentric layers like an onion, which form around the axon terminal.

The lava formed pillow-like bodies which have an internal structure of concentric layers.

The end of this thumb-sized object holds a sphere built in many concentric layers.

Breit floated above three concentric layers of Soviet strongholds, each more formidable than the last.