Along with divine sanctuaries and public buildings, walls were one of the most important features of cities in Greco-Roman antiquity. Cities continued to form the backbone of political, military and ecclesiastical administration in Late Antiquity, and fortifications were thus of primary concern for the imperial authorities. According to Procopius ’ renowned work On Buildings, Justinian did more than any of his predecessors to reorganize the empire’s strategic defence plan: he spent money on rebuilding the walls of many ancient cities and established or strengthened fortifications at strategically important sites. Indeed, these formed part of a unified grid, so as to secure the defence of roads and trading hubs at the same time.

However much these efforts assisted imperial cities, decisive changes to the form they took were wrought by the political and economic downturn that set in from the late 4th century, together with enemy raids, natural disasters and epidemics. Cities diminished in size as their populations shrank; some were completely abandoned, while others re-established themselves or moved their population to different locations nearby, away from plains and the coastline. Such locations were to be found on steep-sided hills or peninsulas connected to the mainland by a narrow isthmus, with a few strategic checkpoints to safeguard the residents from enemy attacks on land and by sea. In all cases there had to be a plentiful supply of drinking water in peacetime or when under siege. Other necessary conditions for founding a city included ready access to arable land, quarries and forests for felling.


Walls – Castle Building

Although the organization of fortifications originated in earlier building tradition, a substantial and somewhat original contribution to castle building was made at this time, involving the reinforcement of specific points depending on the terrain and the susceptibility or vulnerability of the walls. The fundamental objective of fortifications was to repel any attack by creating a series of large barriers to secure defence. Thus, the number and height of walls, the shape and form of towers, the number of gates and their guard systems all depended on the lie of the land, developments in warfare and current economic and building potential.

Walls were as a rule made up of towers and curtain walls. The towers were round, triangular, rectangular or polygonal and had two or more floors. At the top they had a row of crenellated battlements and gun-loops or machicolations through which the defenders could pour boiling water, oil or lead on the attackers. Curtain walls were high and thick enough to withstand attacks by siege engines. At the top they had crenellations, behind which there was a corridor (ambulatory) to allow for troop deployment and movement as well as for access to the towers. Behind the walls were stairs leading up to the battlements, below which there were stores for military supplies and guard rooms. Cities built on plains had another lower wall with towers at intervals (an enceinte) in front of the main fortifications. In front of this was a moat filled with water, which was the first line of containment the enemy came to.

Inside the city, the acropolis or citadel was retained as the highest point in the settlement, with a special wall for defensive autonomy. This was the final refuge for defenders and housed the headquarters of the church hierarchy and military command. The towers on the acropolis also served as observation points, given that their location at the highest point allowed for surveillance of the entire area. From as early as the reign of Justinian, and more systematically in subsequent periods, an intermediate wall with a special gate divided the city into two parts, the upper town and the lower town.  Mystras is an example of a tripartite castle: the intermediate wall secured a second line of defence and protected the quarter housing the despots’ palaces and aristocrats’ mansions.

The gates were founded at the most accessible and thus most vulnerable points, where the main roads from the hinterland met the main thoroughfares in the town plan. This explains why there were few gates, affording effective control over people, vehicles and products entering and leaving the city. The gates opened at sunrise and closed at sunset. On the outskirts of cities there were often hostels with stables for animals and stores for goods, as well as bath houses and inns to accommodate travellers. Inside the walls there were few main streets; most were rather narrow alleyways between houses that stood check by jowl. In a few places, usually next to churches, haphazard planning resulted in open spaces that functioned as squares.

The walls around Constantinople are an excellent example of fortification. This ambitious project was initiated by Theodosius II in 412-413, as the walls of Constantine the Great no longer sufficed- either on account of problems relating to static stability and construction or because of an apparent jump in the capital city’s population. The new wall was supplemented by sea defences and large outdoor cisterns, such as those dedicated to Asparos and St. Mokios, which guaranteed water supply for as long as any siege could last. The fortification consisted of the moat, the enceinte and the 12 metre high main wall. The new walls of Constantinople took in an area of approximately 1,400 hectares and were more than 60 kilometres long. Over the course of centuries they were repeatedly repaired at various places, but lasted for more than one thousand years before being knocked down by the first cannonballs fired by the Ottomans in 1453.


Fortresses and towers

Fortresses and towers were fortifications based on the idea of successive lines of defence, organized in a similar manner to those of city-castles. Their aim was to control strategically important sites and passes as outposts, while at the same time serving other needs, such as storage spaces for agricultural produce from neighbouring areas, quarters for the local ruler, and shelter for the residents of surrounding villages in time of danger. Also, since they were located in the jurisdiction of a castle or monastery they played a significant part in defending wider geographical areas, as forts to check enemy advances or as surveillance points that could warn of imminent dangers.