It is a common tactic using ditches in pre-modern times and explosives or mines later. Simply switch from noun to verb.

explanation here:

http://www.1911encyclopedia.org/Retrenchment

here's one example

http://www.newrosstc.ie/nr/PhotoGallery/Description,6581,en....

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Note added at 13 mins (2012-09-05 15:52:31 GMT)
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the idea is that even if an attacking army succeeds in getting over the outer wall it will then find itself in a trench that is raked by fire from the second defensive wall.

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Note added at 14 mins (2012-09-05 15:52:58 GMT)
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this is called a "dry moat" in English.

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Note added at 19 mins (2012-09-05 15:58:27 GMT)
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"interrompe una strada": in this context the "strada" is not a road but a line of attack.

Spons' dictionary of engineering, civil, mechanical, military, and naval; with technical terms in French, German, Italian, and Spanish has the following entry:

ABATTIS. Fr., Abattis; Ger., Verhau, Verhack; Ital., Abbattuta, Tagliata; Span., Abatis.

An abattis is generally constructed with large branches of trees, sharpened and laid with the points outward, in front of a fortification or any other position, to obstruct the approach of assailants. Abattis should be so placed as not to be exposed to the fire of artillery. In redoubts or entrenchments they are usually fixed in an upright position against the counterscarp, or at the foot of the glacis, the plane of which last is broken so as to permit of their being laid out of the enemy's sight, and so as not to interfere with the musketry fire from the parapet in their rear.
See Fig. 6. An abattis is an excellent mode of blocking up a road; and when the branches are well and properly placed, and interwoven one with the other, the disengagement of them is extremely difficult, and to form an opening sufficient for the passage of artillery, or even of cavalry, requires a long time. An abattis can easily be made by a few men, with half-a-dozen felling-axes and a cross-cut saw, and in a short space of time, if trees of sufficient size are near, or on the spot. It is more easily formed and gives more effective defence than palisades.

An abattis should not be planted out of musketry-range; for this and all other obstacles are to break up the order of the enemy's advance, to impede and keep him under musketry fire. The application of the abattis should be considered aa purely local and not one of the common resources for securing entrenchments, such as palisades, chevatix-de-frise, and fougasses, the materials for the construction of these last being capable of conveyance from a distance. Hence localities may
enable the engineer to obstruct a road, by dragging trees from the hedge-side and connecting the defences of a position, by levelling groups of trees with their branches towards the enemy.

Shrubby trees are not adapted to form a good abattis: they are easily forced and drawn out by the hand. Heavy trees with the trunk cut half-through form insurmountable obstacles; this last is called an Entanglement.