defensive structure
defense ****
defence

It is now part of a 14th-century defensive structure.

It is built on the site of an 11th-century defensive structure.

The tower was built as a defensive structure with a small number of narrow windows.

Over the next ten years, they built a defensive structure around the manor.

The tower was the main part of a four towers defensive structure, built in the 14th century.

There is though some question to what extent it was meant as a defensive structure.

As a result of that, you could examine a defensive structure, and work out why it existed.

I have to say that it's a very reassuring defensive structure.

It remained a defensive structure up until the 13th century.

In some cases elaborate walls or defensive structures were built.