Defensive structure and Line of defense

Defensive structure noun - A structure used to defend against attack.

Line of defense and defensive structure are semantically related. In some cases you can replace phrase "Line of defense" with "Defensive structure", this phrases are similar.

Line of defense noun - Defensive structure consisting of a barrier that can be employed for defense against attack.

Defensive structure and line of defense are semantically related. Sometimes you can use "Defensive structure" instead a noun phrase "Line of defense".