What Makes a Bastion

While the fire from one cannon may have an effect, fire from two on the same attacker would have a improved chance of scoring hits.  From three - or four - even better!  With bastions sticking out from the core of the fort, cannon mounted on them could not only lay down overlapping fields of fire but also intersecting fields of fire from two neighboring bastions.  The enemy could be caught in a crossfire.  Plus, should a cannon or two be silenced, defenders still could cover the field before them.

The successful bastion not only protected itself from every place an attacker could strike it but also its adjoining ramparts and - very important - neighboring bastions.  The mutual support of bastions, with one being able to lay down protective fire for another, was why this concept became so successful and so widely adopted. What an observer immediately notices is the arrowhead-like shape of the bastion, with straight sides, not curved.  Straight sides allowed fire to be directed by defenders along any portion of its sides and out onto the ditch and ground beyond; there was nothing sticking out to interfere with lines of fire, no places to shield attackers.  If attackers at the base of a wall or tower could not be reached by defensive fire, then they could be free to tunnel under to undermine or set explosives.  As mentioned earlier, the round tower of the medieval castle/fort did leave blind spots for defensive fire.  But a bastion with incorrectly angled sides also afforded protection for attackers.

Artillery On the Bastion
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One bastion protected other bastions at either side. Atop those short faces, defenders could mount cannon to blow away any attackers on the walls or the side of the adjacent bastion. If the bastions were within 250 yards / 220 meters of each other, musket fire could also be brought to bear on anyone assaulting an adjacent bastion; in the Netherlands, bastions were usually set within 250 yards of each other specifically to make use of muskets.  These angled bastions set at intervals along the walls offered an effective and deadly system of mutually supporting fields of fire.
 

These illustrations show the defender's cannons firing into their own ramparts.  Did they really do that? 

Yes.

What Came Out of the
Cannon's Muzzle
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Not commonly with cannonballs, however.  Preferred was canister shot.  Any piece in canister shot was not large enough to damage the defensive works but all together certainly sufficient to, um, shred groups of attackers; in modern parlance, it was "anti-personnel."  The "shot cones" displayed in the bottom interactive illustration are meant to suggest patterns of canister shot across target areas.

Aware of the potential of canister shot, attackers were hesitant to swarm up the sides of ramparts unless the defender's cannons were already silenced.

What a Real Bastion Looks Like Dig down

Between the angled planes of the bastion and the ramparted walls, there were narrow faces set usually 90 degrees to the walls, especially for earthen bastions constructed in the Netherlands. These were frequently referred to as 'flanks.' When the bastion was built of masonry, these faces could be inset into the base of the bastion. Inset or not, that little space afforded defenders virtual immunity from enemy fire unless the enemy got very close to the fort.

Ramparts set LESS than 90 degrees to one another proved to have the better ratio of shooting lines to adjacent bastions.  A common bastion-to-bastion angle was 72 degrees.

What did that do for the shape of a fort?

Back	Fort Shape