The angular design was so that guns were in place to sweep attackers from every wall. That is, some of the guns are able, without having to be moved, to fire close to and parallel to every wall.
No attacker would be able to rush the wall and remain there in relative safety (given the benefit of covering fire) and set to work breaching the wall.
Note the "Plan of Johnston Fort at Cape Fear", where the angle of the top left point seems to be inaccurate, such that the covering cannon at the base of the upper right point can't quite shoot along the wall of the upper left point.
Also note the Bristol Ferry Fort, with it's not-quite-star design, can't quite protect the small sides of the points, given the angles of the gun ports (if accurate.)
Also it seems interesting that the designer of the Ontario Fort has put heavier walls toward Lake Ontario, where ship cannon may be used by an attacker. It was the opposite case in Pittsburgh, where one would expect the main attack by land.
No attacker would be able to rush the wall and remain there in relative safety (given the benefit of covering fire) and set to work breaching the wall.
Note the "Plan of Johnston Fort at Cape Fear", where the angle of the top left point seems to be inaccurate, such that the covering cannon at the base of the upper right point can't quite shoot along the wall of the upper left point.
Also note the Bristol Ferry Fort, with it's not-quite-star design, can't quite protect the small sides of the points, given the angles of the gun ports (if accurate.)
See http://en.wikipedia.org/wiki/Star_fort
Also it seems interesting that the designer of the Ontario Fort has put heavier walls toward Lake Ontario, where ship cannon may be used by an attacker. It was the opposite case in Pittsburgh, where one would expect the main attack by land.