La Verdadera Destreza is an esoteric school of rapier fencing born in Spain in the early sixteenth century. The name translates roughly as "The true art and skill", and the style is sometimes referred to as The Mysterious Circle or the Spanish Circle.
The basics of the style are simple and quite elegant. The fencer ("diestro") stands sideways to the opponent, fully upright, with their sword pointing directly toward the opponent at full extension. As long as the fencer maintains this guard, the opponent cannot approach without becoming impaled on the outstretched blade. Because the direct path is blocked, the fencers typically move in a circular pattern, attempting to gain control of the opponent's blade before stepping into distance for an attack. Attacks can be both thrusts and cuts.
The fact that the fencer's posture forms a right angle is not a coincidence. Geometry and mathematics are central to this style of fighting, and in the historical manuals the authors brag about their mathematics teachers almost as much as their swordmasters. The style is often presented in mathematical metaphors: angles, tangents, and chords. A circular diagram was commonly used to illustrate the movements and angles of attack in period manuals. Some teachers of the art recommended drawing the circle on the ground in order to facilitate learning and this digram led to the school's nickname, "The Mysterious Circle". Masters of the Spanish Circle were esteemed as some of the best fencers in Europe.
An excellent series of articles by Maestro Ramon Martinez, a modern instructor of la Destreza, can be found at: http://www.martinez-destreza.com/articles/spanish1.htm