Trace. In general they had a polygonal shape, with
the head front curved outwards, two lateral fronts parallel to the central
redoubt and the gorge front perpendicular to it. Most of them were trapezoidal in shape,
some semicircular, one circular (X) and two circular with a triangular
outwork (ravelin) in front (XIII and XX).
Profile. The firing line was 4-5 m height; the thickness of
the parapet was from 4.5 to 6.5
m. The forts were surrounded by a ditch, 4-5 m depth and 5-10 m width, without scarp
and counterscarp covering, their banks being stiffened as soon as the ground
allowed. Above the counterscarp some forts had a covered way, usually
protected by traverses of earth bags and provided with wooden shelters of
German type, dug into the glacis. Sometimes they were covered by a plate of
corrugated iron. The ditches had no flanking works and were exposed to the
enemy fire, being entirely in the dead angle without any protection.
Defences. The forts were defended
only by infantry, exceptionally supported by some old machine guns. The
ramparts were originally arranged only for open air artillery emplacements.
Therefore it was almost impossible for the defenders to serve their guns
under the enemy fire, and in 1912 the Turks had remove all their guns from all
the forts, except for new Taš Tabia, placing them
in flanking batteries. The main rampart had 3-6 traverses exceeding the crest
of the parapet by 1-1,5 m.
Many traverses covered a vaulted shelter, 60 cm – 1 m thick, made of brick or
stones. Some forts were arranged with two, occasionally also three, lines of
fire, by raising a cavalier on the rampart. The covered ways were usually
well conformed to the ground, and sometimes were not parallel to the firing
line. The bulk of the troops charged of the forts defence were kept behind,
in concrete or wooden shelters, in tents or in barracks, leaving only a
little detachment as permanent garrison. The interval between the forts was
covered only by the infantry firing from the lateral fronts and by the direct
fire of the troops in the trenches and batteries, linking the forts.
Shelters. The shelters were
composed by the casemates built under the traverses of the forts and by the
housing buried under the rampart of the gorge front. The casemates originally
planned to lodge the garrison, in 1912 were usually employed as ammunition
depots. They were made of brick or stones, with vaults 60 cm – 1 m thick near the keystone.
The housings of the gorge front were entirely covered by earth and were
ventilated only by vertical vents, debouching above the ramparts. Their entry
was placed sideways, on the left and on the right of the entry of the fort.
In addition there were the wooden shelters of the glacis.
Communication. The entry of the fort,
wide, was on the gorge front, the rampart being cut by vaulted postern or,
more frequently, simply by an open passage. The gorge ditch was interrupted
in front of the fort entry. Outside it was protected by an outwork for the
infantry, with the form of an arc or, at Aivas Baba, of a triangle, but
without any kind of hindrances before. Inside the forts the ways
communication were uncovered, the inner terre-plein was connected with the
fighting positions by means of ramps.
Trace. Even if designed forts, they were actually
lunettes, having no gorge front and therefore no defence on the back. They
were simply trenches with a straight head front with two sides as lateral
Profile. The height of the firing
line was usually weak, being not higher than 1 m, the slopes, with an inclination
from 1/6 to 1/10, were prolonged below the ground. A grid of barbed wire
placed on the slope, surrounded the head and the lateral fronts. Behind the
fighting position, an inner trench, 2 m wide at the utmost, was employed as
communication trench. There were no flanking works, like in the old forts.
Defence. The forts were defended
by infantry, kept in concrete shelters placed under the parapet, 40-50 cm thick. They were not
made by true reinforced concrete, as the Bulgarian Army thought, since only the
top of the shelter was reinforced by a trellis of 8mm iron wire, while the
front and the lateral walls did not have a metal structure. They were closed
by wooden doors. The fighting position was provided with traverses both
covered by earth and made by earth bags. During the combat, the troops were
deployed behind the traverses placed between the shelters. In some forts a
machine gun was installed in the corner angles (salients), protected by
semicircular parapets reinforced by earth bags.
Shelters. Beside the concreted
shelters of the parapet, the garrison was lodged in concrete shelters placed
behind the forts, just below the crests.
Communication. The links between the
outworks and the forts were out of the enemy sight by means of the ground
features or protected by communications trenches. In the forts themselves the
trench behind the firing position allowed the troops to move without danger.
At the ends of the forts some ramps connected the bottom of the inner
trenches with the level of the ground.
connecting trenches had a weak profile, being high only 80 cm, with the slope
prolonged till the level of the ground. They had only wooden shelters, whose
roof was usually a plate of corrugated iron
2mm thick, covered by earth, in order to protect the troops against the
shrapnel bullets. Sometimes in the rear there were covering trenches linked
with the first line for the communications. To deceive the enemy, the Turks
had also built some fake trenches before the interval between the forts.