Continuous Bastion and Redan Line Across Whitemarsh Island, Georgia. Southeast of Savannah, Georgia.

Bastion lines were an attempt to transfer all the advantages of the flanked disposition to the fortification of extended positions. When properly laid out on a sufficiently grand scale every foot of ground in the immediate front of a line of bastions connected by straight curtains could be defended by two or more columns of fire and no part of the line was beyond the reach of flanking fire. Bastion lines were, as might be expected, the acme of linear traces, but, by the same token, the trace was only considered to be as good as the expense bestowed on its construction, maintenance, and manning, all of which were considered a bit too pricey for just any extended position. For the purposes of comparison the instructions given below reduce the length each front of fortification to a very scant 100 yards. Most engineering manuals of the period claimed that effective flanking could not be achieved on bastion fronts less than 250 yards, given a more or less standard profile that placed the interior crest 8 or 10 feet above the bottom of the ditch, but the simple fact is that bastion fronts of fortification were actually used effectively during the American Civil War on fronts of 100 yards and less.

Begin by drawing a right line of any length and dividing that line into as many segments as the number of bastion fronts of fortification that may be desired. In this example each front has been taken as 100 yards long.

Bisect each front of fortification and construct a perpendicular line toward the interior side of the line that is equal to one-sixth the length of the front. On fronts 100 yards long the perpendiculars will be 16 yards long (actually 16.66 yards, rounded down to 16 yards for convenience).

Produce the lines of defense by drawing right lines from each extremity of a bastion front through the interior extremity of its perpendicular. These line should extend most of the way to the capitals of the bastions or at least far enough to use them to establish the the positions of the bastion flanks and angles of the curtains.

Establish the bastions' faces by taking a length equal to two-sevenths of the front of fortification along the lines of defense starting from the extremities of each front of fortification. With fronts 100 yards long the bastion faces will be 28 yards long (actually 28.57 yards, rounded down for convenience).

Next come the bastion flanks. In this case the flanks will be made perpendicular to the lines of defense by dropping perpendiculars from the interior extremities of the bastion faces to the lines of defense immenating from collateral extremities of the fronts of fortification. This produces flanks that are slightly over 14 yards long.

Finally, the curtains are drawn by producing lines from the interior extremities of one bastion flank to the next bastion flank. On a front of 100 yards this construction produces flanks that are approximately 40 yards long.

It may also be noted that a continuous line of bastions may easily be converted into a line of detached lunettes by simply suppressing the curtains that join the bastions together.