Finnish officer cadets learn how to create a giant abatis as part of their countermobility course. The trees are felled at a 45° angle over the road from alternating sides which makes the interlock. In a country covered by forests many secondary roads are suitable for abatises, and while it is far from unbreachable, properly done it can cause significant delays for an advancing enemy. The fact that no additional building material is needed also means that it is one of few means an infantry unit can employ to quickly create a serious obstacle without the need for heavy machinery. Picture source: KAIPR FB