The area's natural defences led to it playing a role in the military history of England.

It was her natural defence after her early years of domestic service.

And Brian felt like he had no natural defences against such an invasion.

The surrounding bogs provided a natural defence for the village.

It had five sides, or four plus the southern side, which was a natural defence.

The contours of the land provide excellent natural defences to the north and east sides.

In the subsequent battle the Christians made use of the natural defences.

In the skin the natural defences against infection are reduced.

But the steroid she took hampered her body's natural defences.

I'm afraid it's mainly a matter of waiting until their own natural defences beat off the viruses that cause it.