2. Britain

How Britain has defended its coastline for nearly a thousand years since the Norman invasion – seeing off threats from Napoleon to Hitler.

3. Poland

The story of how Poland, one of the most invaded countries in Europe, has survived against all the odds.

4. The Netherlands

The story of how the Netherlands, locked in a constant battle with water, has harnessed this threat to become a powerful European player.

5. France

Discovering how France constructed ingenious fortifications, on a massive scale, to defend itself against attacks from the east.

6. Spain

The impressive fortifications and defensive strategies used during Spain’s dramatic history of conflict, from the Middle Ages to the Civil War.