What were the characteristics of trench warfare?

Question

Also a question on World War I

Answer 1

Lots of trenches (for the soldiers to duck into).

Answer 2

Absence of mobility and resilience on heavy artilery , machineguns and costly infantry assaults. In other words, flesh against steel and lead. Pehaps the most futile form of warfare known to the entire human history as the losses of the Word War I could testify. For example in the opening day of Somme (1 Jully 1916) the British suffered 60% casualties
(60.000 dead, missing, wounded and prisoners out of 100.000 troops engaged)