https://en.wikipedia.org/wiki/Battle_of_Doiran_(1917)

In 1917 the Bulgarian defensive positions and fortifications were further improved. It included two prime positions with two rows of continuous trenches 1.5 – 2 metres deep, 200 to 1000 m apart and linked with passages for communication. In front of these positions was a two-line system of wire entanglements. Between the rows of trench watchpoints, shelters, machine-gun nests and sunken batteries were constructed. Behind these defences were concrete galleries, artillery encampments, and ammunition platforms. There were smaller fortifications in front of the primary position, with a partly constructed secondary position 2 – 5 km to its rear.

The battle for a breakthrough in the Bulgarian positions began on 22 April and continued intermittently until 9 May 1917.

Though the artillery duel continued until 9 May, the British had to abandon all attacks due to heavy casualties. They lost 12,000 killed, wounded and captured, of which the Bulgarian defenders buried 2,250. The losses of the [Bulgarian] Ninth Pleven Infantry Division were 2,000, of whom 900 died from disease and wounds.[8]

ROW ON ROW, AS THEY COME FROM BELOW

TWICE THEY ATTACK, TWICE THEY'RE BEATEN BACK!

EVERY TIME THEY TRY, THEY WILL DIE!

THE LINE OF DEFENSE STILL INTACT