The Castle of Guimarães was built under the orders of Mumadona Dias in the 10th century to defend the monastery from attacks by Moors and Norsemen. At the end of the 11th century the castle was heavily expanded and remodeled, under the direction of Count Henry, to act as his residence. The castle became the official royal residence from 1139, when Portugal became independent from the Kingdom of León, until circa 1200.
Between the end of the 13th and beginning of the 14th century, the castle was remodelled by King Denis, resulting in the form that stands to this day. In 1369, King Henry II of Castile invaded Portugal and encircled the castle of Guimarães, but was defeated by its population and forces. Sometime between 1383 and 1433, the two towers that flank the main entrance were order built by King John I of Portugal.
After the castle's demolition was abandoned in the 19th century, many of the houses, estates and lodgings around the castle were expropriated. The first attempts at restoration occurred during the mid-20th century.
Today Guimarães castle area is delineated by walls forming a pentagram, similar to a shield, that includes eight rectangular towers, military square and central keep. Originating in the foundations of a Roman structure, from the writings of Alfredo Guimarães, it was later elaborated on the French model, in its current the form of a shield, with reduced central yard and difficult accesses. It includes several Gothic characteristics, owing to its remodelling at the end of the 13th century, when the keep and residences were constructed (possibly over pre-existing structures).
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.