The structure of defenses changed radically between the 14th
and 18th centuries as cannons gained more widespread adoption
as siege weapons.
Cannons more or less made the previous defensive structure of high stone walls,
such as those surrounding castles or walled cities,
completely useless. A new defensive structure had to evolve. One of the
more successful structures was called the battlement. However, the
lower walls of battlements and the longer range nature of cannon
sieges left the defender at a disadvantage to covering the battlefield
defensively by creating a number of blind spots:
\ o o /
| I I |
o==| - - |==o
o==| _ _ |==o
| I I |
|==o is a cannon.
The Italians created the following geometrically-based solution:
o / \ o ^
\ / o / \ o
/ \ \ /
\ ==o / \
/ /-__ o== /
o \ --__ \ \
/ --_\ / o
o / |
/ / |==o
This design reduced or eliminated the effective blind spots on the
battlefield by increasing the number of sides the defensive structure
had. The term "Trace Italienne" is French for "Italian Shape (outline),"
as it was the French who first encountered this structure on the
battlefields of northern Italy.
This shape proved to be very successful, indeed many American forts display this
design. Even the American Pentagon Building
exhibits ideas from this enlightened design.