A fortified tower is one of the defensive structures used in fortification

Fortification

Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...

s, such as castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

s, along with curtain wall

Curtain wall (fortification)

A curtain wall is a defensive wall between two bastions of a castle or fortress.In earlier designs of castle the curtain walls were often built to a considerable height and were fronted by a ditch or moat to make assault difficult....

s. Castle towers can have a variety of different shapes and fulfil different functions.

Shape of towers

Rectangular towers

Square or rectangular towers are easy to construct and give a good amount of usable internal space. Their disadvantage is that the corners are vulnerable to mining. Despite this vulnerability, rectangular towers continued to be used, and Muslim military architecture generally favoured them.

Round towers

Round towers, also called drum towers, are more resistant to siege

Siege

A siege is a military blockade of a city or fortress with the intent of conquering by attrition or assault. The term derives from sedere, Latin for "to sit". Generally speaking, siege warfare is a form of constant, low intensity conflict characterized by one party holding a strong, static...

 technology such as sappers and projectile

Projectile

A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....

s than square towers. The round front is more resistant than the straight side of a square tower, just as a load-bearing arch

Arch

An arch is a structure that spans a space and supports a load. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.-Technical aspects:The...

. This principle was already understood in antiquity.

Horseshoe-shaped towers

The horseshoe-shaped (or D-shaped) tower is a compromise that gives the best of a round and a square tower. The semicircular side (the one facing the attacker) could resist siege engines, while the rectangular part at the back gives internal space and a large fighting platform on top. The large towers at Krak des Chevaliers

Krak des Chevaliers

Krak des Chevaliers , also Crac des Chevaliers, is a Crusader castle in Syria and one of the most important preserved medieval castles in the world. The site was first inhabited in the 11th century by a settlement of Kurds; as a result it was known as Hisn al Akrad, meaning the "Castle of the...

 and the gate tower

Gate tower

A gate tower is a tower built over or next to a major gateway.Usually it is part of a medieval fortification. This may be a town or city wall, a fortress or a castle. The gate tower may be built as a twin tower on either side of an entranceway. Even in the design of modern building complexes, gate...

s at Harlech

Harlech

Harlech is a town and seaside resort in Gwynedd, within the historical boundaries of Merionethshire in northwest Wales. Lying on Tremadog Bay and within the Snowdonia National Park, it has a population of 1,952, of whom 59% speak Welsh...

 are good examples. Armenian castles such as Lampron

Lampron

Lampron - is a castle near the town of Çamlıyayla in Mersin Province, Turkey. While part of the Armenian Kingdom of Cilicia in the Middle Ages, the castle was known as Lampron and was the ancestral home of the Armenian Hethumid princes...

 also favoured this style.

Polygonal towers

A common form is the octagonal tower, used in some bergfried

Bergfried

A bergfried is a tall tower typically found in medieval castles in German-speaking countries . Its defensive function is to some extent similar to that of a keep or donjon in English or French castles...

s and at Castel del Monte in Italy.

There are also hybrid shapes. For instance, the keep at Château Gaillard is round, but also has a triangular beak to deflect projectiles.

Towers with specific functions

Wall towers provide flanking fire (from crossbow

Crossbow

A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts or quarrels. The medieval crossbow was called by many names, most of which derived from the word ballista, a torsion engine resembling a crossbow in appearance.Historically, crossbows played a...

s or other projectile weapons) to a straight part of the curtain wall. Corner towers enfilade the two adjoining wall faces. If corner towers are far apart, additional flanking towers may be added between them. Towers in an outer curtain wall are often open at the back.

Particularly large towers are often the strongest point of the castle: the
keep

Keep

A keep is a type of fortified tower built within castles during the Middle Ages by European nobility. Scholars have debated the scope of the word keep, but usually consider it to refer to large towers in castles that were fortified residences, used as a refuge of last resort should the rest of the...

 or the bergfried

Bergfried

A bergfried is a tall tower typically found in medieval castles in German-speaking countries . Its defensive function is to some extent similar to that of a keep or donjon in English or French castles...

. As the gate is always a vulnerable point of a castle, towers may be built near it to strengthen the defences at this point. In crusader castles, there is often a gate tower

Gate tower

A gate tower is a tower built over or next to a major gateway.Usually it is part of a medieval fortification. This may be a town or city wall, a fortress or a castle. The gate tower may be built as a twin tower on either side of an entranceway. Even in the design of modern building complexes, gate...

, with the gate passage leading through the base of the tower itself. In European castles, it is more common to have flanking towers on either side of the gatehouse.