Complex sentence: Axis engineers refurbished the Mareth Line for occupation by the "Panzerarmee" and by March 1943, more than of barbed wire, 100,000 anti-tank mines and 70,000 anti-personnel mines had been laid, bunkers had been reinforced with concrete and armed with anti-tank and anti-aircraft guns.
Split into simpler sentences: Axis engineers refurbished the Mareth Line for occupation by the "Panzerarmee". By March 1943, more than of barbed wire, 100,000 anti-tank mines and 70,000 anti-personnel mines had been laid, bunkers had been reinforced with concrete and armed with anti-tank and anti-aircraft guns.