Cēsis Castle (German: Schloß Wenden) is one of the most iconic and best preserved medieval castles in Latvia. The foundations of the castle were laid 800 years ago by the Livonian Brothers of the Sword. The most prosperous period Cēsis Castle experienced was during its next owners, the Teutonic Order. It became one of the key administrative and economic centers of the Teutonic Order in Livonia and was the seat of the Landmeister in Livland. The first serious damage was done to the castle during the Livonian War, when it was besieged by the army of Ivan the Terrible. In the course of the siege of 1577 approximately 300 people within the castle committed mass suicide by blowing themselves up with gunpowder. Cēsis Castle was still in use during the following century but it fell into disuse after the Great Northern War. Today the castle is the most visited heritage site in Cēsis and one of the 'must see' destinations in the Baltic states.

In the autumn of 1206 during the Livonian Crusades, the Wends (a small tribe living on the site of the present day town of Cēsis) converted to Christianity and became allies of the crusaders. In 1208 the Brothers of the Militia of Christ, otherwise known as the Livonian Brothers of the Sword, took up residence among the Wends in their hillfort. They fortified the Wends' hillfort with a stone wall, largely replacing the previous timber defences. Although the Chronicle of Henry of Livonia describes the fort as “the smallest in Livonia”, it withstood repeated sieges by Estonians and Russians.

In 1213 or 1214 the Livonian Brothers of the Sword started construction of the new stone castle right next to the Wend's hillfort. The design of this 13th century castle is unknown as all its structures (except the chapel) have been torn down in the course of the subsequent building phases.

In 1237 Cēsis Castle was taken over by the Livonian branch of the Teutonic Order. Under the new governor Cēsis Castle underwent large-scale reconstruction. The old fortifications were gradually replaced by a monumental square castle (castellum), consisting of four ranges built around a courtyard. This form of the Teutonic Order castle was imported from Prussia and largely stemmed from the need for “fortified convents” that would be easy to defend and where the brethren's domicile would be as compact as possible. To provide additional safety and accommodate various service buildings, outer baileys were built as part of the castle complex. As a result of the grandiose reconstruction Cēsis became one of the largest and mightiest castles of the Teutonic Order.

The convent of Cēsis Castle was under the charge of a high-ranking Teutonic Knight – commander or Komtur. The Komtur was responsible for adequate supply of the brethren with food and armament, for order and discipline in the castle and for the collection of dues within the castle's district – Komturei. At the beginning of the 15th century Cēsis Castle and Komturei came under the direct rule of the Order's supreme commander in Livonia, becoming part of the-so-called Livonian Master's district. However, for most of their time the Livonian Masters resided in Rīga Castle, but in periods of danger and instability they moved to Cēsis. Finally, at the end of the 15th century, the Order's administrative headquarters were relocated from Rīga to Cēsis, and Cēsis Castle became the permanent residence of the Masters.

As the residency of the Livonian Master and the meeting place of the Order's highest officials in Livonia Cēsis Castle witnessed many events of great significance for the history of Livonia. Here envoys were received, issues of war and peace decided and it was here that the Order's troops assembled for military action when such need arose. The castle also housed the Order's archives and library as well as a chancery with a scriptorium.

The period from 1494 to 1535, when the Livonian branch of the Order was led by Wolter von Plettenberg – one of the greatest politicians and military commanders in Livonia's history – is traditionally considered as the time of the greatest flourishing of Cēsis Castle. Under von Plettenberg Cēsis Castle underwent large-scale reconstruction. The castle's fortifications were reinforced with three artillery towers, while some of castle's interiors (e.g. the Chapter Hall and the Master's Chamber) underwent major remodelling. Resplendent Master's Chamber brick vaulting from c.1500 survives up to now.

The ongoing development of Cēsis Castle was interrupted by the dissolution of the Teutonic Order's Livonian branch in 1561 and by devastating sieges of the castle that took place during the Livonian War. In 1577, when the castle was besieged and bombarded for five days by the army of Ivan the Terrible, 300 people within the castle, realizing that it will be impossible to defend themselves any longer, made the decision to commit a mass suicide by blowing themselves up with four barrels of gunpowder. In 1974 archaeologists unearthed two basement rooms, which had remained over from the castle's western range – the part of the castle that collapsed as a result of explosion. On the basement floor under the collapsed ceiling beams a number of human remains of adults and children were uncovered, all securely dated by coins to 1577, Chronicler Salomon Henning reports that 'all were blown up, aside from those who were hiding elsewhere in the castle' and it is likely that human remains recovered by archaeologists belonged to those who were trying to avoid the explosion.