"This is the segno, where you'll make your students walk, stepping forward as well as back, with weapons in hand, round about, putting their feet on the edges that cross the segni tondi (round signs)."
There are three principles that guide all combat in the Italian system.
1) Principle of Expansion/contraction
2) Principle of Angulation
3) Principle of the hand & foot.
Along with the principles are three distances
1) Normal – with swords extended the tip of the sword is at your opponent's guard
2) Close – With arms extended the guards are together
3) Grappling distance – Hand is inside the inside of the opponent's guard. (Giocco stretto)
The principle of expansion/contraction is that for all attacks you must expand out towards your opponent. Marozzo used the gran passo or great step when making the attack. Later masters such as Fabris taught the lunge. When defending you close the line you are being attacked in. This closing of the line may be considered a contraction. However in 16th century swordplay the arm is not withdrawn in the parry as say done in some schools of modern fence such as the French school for foil.
The principle of angulation states that you will use angle of blade to attack your opponent. Geometry is very important in the Italian system. Opposition is important when dealing with angulation. Opposition may be used on the attack or in defense to take your opponent's point away from you.
The principle of the hand & foot states that the hand and foot must finish movement at the same time on attacks. As the thrust or cut lands the moving foot must land at the same time.
The normal distance is the safe distance where you attack and defend. At normal distance you may also make attacks on advanced targets such as the hand. Close distance is the hot distance where you may wound your opponent. So, at this distance you may strike your opponent's head or torso.
Like the Spanish system the Italian System uses circles to help visualize attack, defense and movement. Unlike the Spanish system the Italian system uses three circles. Each fencer has a circle that they stand in the center of. A third circle lies between the two fencers. During an attack the attacking fencer must take the center circle. To do so he will move on an angle across his own circle while forcing his opponent's blade to the circumference of the middle circle. The defender will also move on an angle across their own circle. The attacker obtains the "triangle" of attack to successfully land a touch on their opponent.
Ideas for this circular theory of fencing were initially introduced to me by IMAF instructors circa 2000 or 2001.