Launched initially in Europe in 1979 and later introduced to North America in 1981, the theme enjoyed continuous support until 1999.

Examples are: one-piece horse, horse saddles, new knight helmets with fixed visors, feather plumes (there were three types in five colors: red, blue, yellow, white and black), waving flags and bows and arrows.

Some fans in the United States have labeled this faction as "Black Falcons", and Australian fans have called them "Eagle Crest", though at the time each term appears only once in any official Lego literature – both in regional names for set 6074.

The sets that would eventually form the basis of the Crusaders were released the same year as the Black Falcons in 1984.

They had shield-like emblems on their torsos, one which was a yellow lion set against blue, while the other emblem had the crossed axes (two black and gold axes crossing each other against a black and gold background, split down the middle, with a red border).

The 1992 United States and Canadian catalogue officially established the faction as the Crusaders.

The King's Mountain Fortress was also the first Lego castle to be mounted on a raised "ramp and pit", baseplate which had debuted the previous year in the pirates set Eldorado fortress and would feature in many subsequent Lego Castle, Pirates, and even Space sets.

Much like the Crusaders, the Black Knights were based on earlier, non-theme-affiliated sets, some of which were retrospectively included in the faction.

Officially launched in 1992, the Black Knights are characterized by a red, yellow, and blue wyvern dragon symbol which is only shown on their shield or flag; unlike the other factions the Black Knights never wore the emblem on their chests.

The Dragon Masters collection was released in August 1993, making it the first time that Lego Castle had a fantasy faction with magic and mythical creatures.

The new dragon animal figure had points of articulation at the jaw, arms, wings, and the tail, with studs on their back to carry a minifigure as a rider, while a flame could be inserted near the tip of its mouth.

Dragon Masters also introduced new knight helmets, halberds, faces, and the Wizard's glow-in-the-dark wand.

The Dark Forest faction is similar to Forestmen, almost as a reboot of the former team, and uses the same shields and iconography.

The Fright Knights were a faction of soldiers that were not ruled by a king, but instead by Basil the Bat Lord.

The Fright Knights Lego Sets delved deeper into the supernatural "Fantasy" aspect of Lego, featuring black dragons with fire-colored wings, creepy trap-filled red-and-black castles, crystal balls and Willa the Witch, a dark sorceress who was the real power behind Basil's throne.

In contrast to Fright Knights, Ninja took its influence from a more realistic starting point and was set in mountainous Japan with medieval buildings.

It is a revamped version of an earlier Knights' Kingdom Lego theme, featuring larger, action-figure like characters as well as more colorfully attired minifigures in the traditional sets.

King's Castle (set 10176) is part of this product line, but is not in the official storyline.

The human faction bears the emblem of a crown, leading to being nicknamed by buyers and Lego fans as the "Crownies".

In 2008, Lego Castle introduced sets with orcs, trolls, and dwarves to add to the medieval fantasy theme.

One side has the role of the attackers, featuring more vehicles and siege engines (The Green Kingdom/Dragon Knights).

The Kingdoms theme was discontinued in 2012, replaced by The Lord of the Rings franchise sets.

Although Lego has not released a new line of medieval-themed sets since the end of Castle III in 2013, Lego has released, under other lines, several standalone sets which are stylistically consistent with many of the previous Castle themes.

In November 2021, a Lego Castle themed land was announced for the upcoming launch of Legoland Shanghai Resort in 2024.