The precise line of demarcation left the upper reaches of many westward-draining valleys in Italian hands, thus giving Italy positions on high points overlooking French territory, those however were most impractical and inadequate.

[4] The plan was altered in 1928 by General Fillonneau, who proposed to concentrate fortifications along potential invasion axes, rather than along a continuous line.

The geographic emphasis remained on Menton and Sospel, but the concept of frontal confrontation was replaced by a strategy of attack from the flanks of a potential advance.

Fillonneau was assisted by the new management organization for the Maginot fortifications, the Commission d'Organisation des Régions Fortifiés, or CORF.

[6] As with the main Maginot Line of the northeast, positions took the form of concrete-encased strongpoints linked by tunnels, which housed living quarters, magazines and utilities for the ouvrage.

Larger ouvrages were provided with 600 mm (1 ft 11+5⁄8 in) narrow gauge rail lines to move materials and munitions, although unlike the northeastern positions, none were electrified.

By comparison, most northeastern ouvrages were semi-submerged into the gently rolling soil with galleries deeply buried beneath earth cover.

In addition to the linked complexes of blockhouses that formed the grand and petit ouvrages, the country around and between each position was provided with isolated blockhouses, observation points, shelters (or abris), outposts (avants postes) and batteries, using much the same vocabulary of rounded concrete forms as the primary line of fortifications.

CORF took over responsibility for construction in 1931, standardizing design practices, although each project was closely adapted to local circumstances.

From 1939, the main d'oeuvre Militaire (MOM) built a number of positions and blockhouses, usually in locations close to the frontier.

Coverage could therefore be reduced compared to the ouvrages of the northeast, which were at depths of up to 30 metres (98 ft) in deep soil to resist heavy siege artillery.

An advance along the main coastal road was delayed by stiff resistance at the Casemate du Pont Saint Louis on the border at Menton, which was manned by seven men led by a non-commissioned officer and was supported by main-line fortifications at Ouvrage Cap Martin.

[23] Two more attacks were mounted, in the areas of Briançon and the Little St Bernard Pass, with little effect due to weather and the difficult terrain.