Despite the fact that it used to be a fortified town, common terminology refers to the settlement surrounded by the fortification of the Castle Hill's plateau of Buda as "the castle" (Castle district, Castle, Buda Castle). The reason for the confusion of terms can be explained by the vibrant history of Buda, in which times of peace and times of war alternated down the centuries.
Following the devastating Mongol invasion of Hungary led by Batu Khan in 1241-1242, King Béla IV. founded the castrum novi montis Pestiensis or castle of the New Hill of Pest on the flat top of the steep mountain directly opposite Pest town, which had been burnt down. 
This secure castle provided a new home for the citizens of Pest settled here by the king. Through this act the king created one of the first fortified towns surrounded by stonewalls in Hungary. With the exception of the struggles for the throne at the beginning of the 14th century, the next three hundred years can be considered as a reasonably peaceful period. This relative peace lead to the town walls gradually losing their significance, thus after the defeat of the Hungarian army at the Battle of Mohács in 1526 no one even thought the walls would be able to offer protection from the sultan's armies. Asa result of this all the townsfolk fled in terror in the wake of the royal court. The town only regained its military significance during the time of the political confusion that followed the Battle of Mohacs, and in 1530 King John Szapolyai with the help of the Turks successfully defended Buda against King Ferdinand of Habsburg. In response to the continuing threat, he also strengthened the capital town by having new ramparts erected. Following the king's death in 1541, the sultan himself seized the town and turned it into the most important border fortification of the Ottoman Empire. During the one hundred and forty-five years of Ottoman reign, one of the most important responsibilities of the pashas of Buda - who at the same time also fulfilled the role of commanders of the castle, - was to continuously build, maintain and develop the fortifications. 
They carried this out so successfully, that Christian troops were only able to reoccupy the castle after a major struggle as late as 1686, and then only after five failed attempts. However, the reoccupied town retained its military significance, and its damaged walls were continually reconstructed right until the second half of the 18th century, by which time neither domestic politics nor the threat of a Turkish invasion justified any further maintenance of the fortification. The castle walls and the army became an obstacle in the way of civil development. In spite of the decreasing military presence, Buda Castle once again gained importance during the Hungarian War of Independence. In 1849 the siege of the castle lasted for several weeks, delaying the advance of the Hungarian army. In the second half of the 19th century, the walls had finally and definitely lost their military significance, and the process of pulling down the fortification system - primarily the gates and some of the towers, - had begun. The outstanding defensive significance of the site was nevertheless demonstrated once again during the siege of Budapest in 1944-1945, during which time the final military resistance of the German troops took place on the Castle Hill, resulting in the veritable destruction of the historical town centre.
Fortification walls erected during the reign of King Béla IV embraced the entire hill plateau tracing the shape of the hill's steep and rocky edge wherever possible. Certain parts of this very first wall are still well known today. Long sections of it were excavated at the western side under the Tóth Árpád sétány in the 1960's. The remainings proved that the walls had been protected by evenly set out towers, eight of which were excavated within this area which goes as far as the Fehérvári Gate. Due to the extensive archaeological investigations pursued south of the gate, the castle wall's entire length is known today as far as the so-called Csonka (Truncated) Tower of the later Royal Palace. Another semi-circular tower was excavated within this section, and a couple more in the foreground of the royal palace (these latter two can be viewed at the so-called Hunyadi Court of the palace). Towers on the western side were built at a 65-70-metre distance from one-another, and it appears that the arrangement of the towers followed the semi-circular and quadrangular plans. Additional remnants of towers were found and excavated under the courtyard of the Museum of Military History (which can also be viewed), and within the area of the State Press, while the remnants of another tower were located near to the Transylvanian Bastion. No tower ruins have been excavated on the eastern side, which is protected by the river, and only certain sections of the castle wall have been unearthed. However, the choirs of three church buildings were also attached to the castle wall: those of the Dominican and Franciscan convents, and in all probability of the parish Church of Our Lady (today's Matthias Church).
The location of the gates also indicates a clear purpose. At the mouth of the valleys that lie alongside the narrow southern part of the hill, two gates used to face each other embracing the town's market place, later named St George's market (today: Dísz tér/Square). On the eastern side facing the Danube stood the St John's Gate (today known as the Vízi Kapu/Water Gate), while on the western side facing the vineyards and the road leading to Fehérvár stood the Jewish Gate. The third gate was Szombat gate on the northern town wall opening from the market place, that is Szombat place (today Bécsi gate), which used to lead to the road to Esztergom. The gate, which was located next to Kammerhof is mentioned in a charter, and the Kreinfeld Gate which obviously opened to the south but no remains indicate its location, is also only known from written sources. All the gates were demolished during the last century, and their excavation is yet to be carried out. The only conclusion that can be drawn from the various illustrations and maps still available to us, is that the gates used to stand on quadrangular plan towers and were located beyond the imaginary straight line of the town's wall, furthermore, that the walls declined to the gate towers.
The plateau used to enclose a shape of a protracted triangle, which meant that the corners required special defence. Remnants of a giant quadrangular plan tower were excavated at the northwest corner, however, these date to a later medieval period, the original closing of the town walls is yet unknown. The so-called Kammerhof, - or the Old Royal House as it is referred to in sources in Latin, - is located at the northeast corner. 
Remnants of the Stephen's Tower, which once stood at the projecting, rocky extension of the plateau at the southern corner, were the starting point of the royal castle construction work pursued in the later periods. It is worth observing, that both the Kammerhof and the Stephen's Tower were located at the edge of the plateau - hence at the edge of the town's fortification, - which leads to the conclusion that at the time of their construction the fact that they formed one block, yet at the same time remained separate and distinct pieces of architecture, was an important point to consider. Both quarters used to stand beside the Danube and rose above the walls and other important parts of the town. The Kammerhof Tower faced the Szentpétermártír quarter of the town and the Felhévíz port, while the István Tower looked down on Alhévíz and its port. Consequently they both used to oversee, and at the same time attract important traffic from the Danube and the ports. In regard to the town's fortifications, both quarters were built in one corner, thus improving the town's defence.
The complete fortification covered a rather large - 400,625 square metre - area, with a wall-length of three kilometres. These dimensions outstripped any previously constructed bailiff castles of the Árpádian Age. Besides its extraordinary size, another characteristic feature it enjoyed was the fortification system consisting of evenly set out towers standing outside the walls, something of a novelty in Hungary at the time.
Around the town wall described above, another curtain-wall was built. Archaelogical investigations to unearth the remnants of this wall were less successfull since it was used for constructing fortification walls throughout the 16th century. Later, this wall endured numerous assaults and underwent repair work, and even nowadays forms the foundations of the wall still standing. This is the reason why it is difficult to study it by archaelogical methods. The wall's most well known section is located on the western side leading from the foreground area of the royal palace to the Fehérvári Gate. Here it can be clearly observed that the curtain-wall was built as a buttress somewhat lower down on the edge of the hill, and sometimes by carving into the hill itself. It used to run along very close to the inner wall, to the extent that in some places the towers of the inner wall touched it by blocking the passage way completely. According to the earliest maps, buttresses at certain sections also supported the walls. Two wall sections with buttresses still stand today, one by the side of the Halászbástya (Fishermen's Bastion) and the other at the southern side of the Erdélyi Bástya (Transylvanian Bastion). The rest of the original wall has already been re-constructed or is obscured from view by newly built wall sections. However with the help of stratigraphy carried out while doing archaeological investigation on the western side of Szent György tér (Saint George Square), on could precise that the wall was built at the end of the Anjou era in the last quarter of the 14th century.
The plateau used to enclose a shape of a protracted triangle, which meant that the corners required special defence. Remnants of a giant quadrangular plan tower were excavated at the northwest corner, however, these date to a later medieval period, the original closing of the town walls is yet unknown. The so-called Kammerhof, - or the Old Royal House as it is referred to in sources in Latin, - is located at the northeast corner. Remnants of the Stephen's Tower, which once stood at the projecting, rocky extension of the plateau at the southern corner, were the starting point of the royal castle construction work pursued in the later periods. It is worth observing, that both the Kammerhof and the Stephen's Tower were located at the edge of the plateau - hence at the edge of the town's fortification, - which leads to the conclusion that at the time of their construction the fact that they formed one block, yet at the same time remained separate and distinct pieces of architecture, was an important point to consider. Both quarters used to stand beside the Danube and rose above the walls and other important parts of the town. The Kammerhof Tower faced the Szentpétermártír quarter of the town and the Felhévíz port, while the István Tower looked down on Alhévíz and its port. Consequently they both used to oversee, and at the same time attract important traffic from the Danube and the ports. In regard to the town's fortifications, both quarters were built in one corner, thus improving the town's defence.
The complete fortification covered a rather large - 400,625 square metre - area, with a wall-length of three kilometres. These dimensions outstripped any previously constructed bailiff castles of the Árpádian Age. Besides its extraordinary size, another characteristic feature it enjoyed was the fortification system consisting of evenly set out towers standing outside the walls, something of a novelty in Hungary at the time.
Around the town wall described above, another curtain-wall was built. Archaelogical investigations to unearth the remnants of this wall were less successfull since it was used for constructing fortification walls throughout the 16th century. Later, this wall endured numerous assaults and underwent repair work, and even nowadays forms the foundations of the wall still standing. This is the reason why it is difficult to study it by archaelogical methods. The wall's most well known section is located on the western side leading from the foreground area of the royal palace to the Fehérvári Gate. Here it can be clearly observed that the curtain-wall was built as a buttress somewhat lower down on the edge of the hill, and sometimes by carving into the hill itself. It used to run along very close to the inner wall, to the extent that in some places the towers of the inner wall touched it by blocking the passage way completely. According to the earliest maps, buttresses at certain sections also supported the walls. Two wall sections with buttresses still stand today, one by the side of the Halászbástya (Fishermen's Bastion) and the other at the southern side of the Erdélyi Bástya (Transylvanian Bastion). The rest of the original wall has already been re-constructed or is obscured from view by newly built wall sections. However with the help of stratigraphy carried out while doing archaeological investigation on the western side of Szent György tér (Saint George Square), on could precise that the wall was built at the end of the Anjou era in the last quarter of the 14th century.
Following the Mongol threat, the extinction of the Árpád dynasty and the end of the struggle for the throne at the beginning of the 14th century, the military significance of Buda decreased. Throughout the 14th century, charters ever more frequently refer to it as a town instead of a castle. The gigantic royal palace, surrounded by modern fortifications that distinctly separated it from the town, was constructed between the 1380's and the 1420's. Written sources from this time onwards apply the name castle to the royal palace, too. At the same time the fortification walls gradually began to lose their significance. Since the number of building plots couldn'be increased due to the fact that the hill had been built in during the 13th century, every inch of space began to be utilised within the walls meet the needs of the growing population. Owners of plots that were located close to the walls expanded towards the curtain-wall. In many cases, the space between the walls was built into, or the wall was simply pulled down. Several of these plots are known from excavations on both the western and eastern sides, and many of them are clearly identifiable on vistas from a later period. Several-storey wing-extensions usually supported by buttresses were built at the back of the plots. In certain cases these extensions reached beyond the line of the outer town wall. Due to recurrent reconstructions the town wall almost completely disappeared, especially on the protected eastern side. Several of these extensions were built right next to each other and can be observed on both sides of St John's Gate. On the slopes of the hill there were farmhouses close to the wall. It is therefore not at all surprising, that the first vista made of the town in the World Chronicle edited by Hartman Schedel, which was rather diagram-like and difficult to use, indicates no town wall whatsoever on the eastern side. It seems that the protection of the western side was given greater emphasis. The woodcut made by Erhard Schön in 1541, indicates on the western side a few defensive buildings, which must have been built onto the town wall at the end of the 15th, or at the beginning of the 16th century. The woodcut clearly indicates that outside the tower of the Jewish Gate, a wall was built with a new gate, and outside the gate stood a massive quadrangular plan gun-tower. Quadrangular plan towers with cannon battlements can also be observed on both sides of the gate. All these details will have to be precised by future archaeological investigations.