Regular building blocks of controlled shape and size can be assembled to create fully dense “architectured” materials and structures. When the building blocks are very stiff and when they interact through much softer materials or even only by frictional contact, the blocks can slide, rotate, separate or interlock collectively, providing a wealth of tunable mechanisms, precise structural properties and functionalities. In this talk I will illustrate this design strategy with three examples: First, I will show how the brick-and-mortar architecture of nacre from mollusk shell exploits near-perfect structural periodicity and geometric hardening to promote large deformations and toughness, which are key features we recently translated into tough, impact resistant bioinspired glasses. In the next example geometric hardening is pushed to the extreme to create geometrical interlocking. Tetrahedral or octahedral blocks are assembled into “topologically interlocked” panels, which can turn brittle ceramics into ductile, tough and damage tolerant 2D panels purely from the interplay of block geometry, interlocking and frictional sliding. Finally, my third example will show how this design principle can be extended to three-dimensional granular crystals. Here we assembled millimeter-scale 3D printed grains of specific geometries into fully dense crystals, which we found are 10 times stronger than traditional granular materials. These granular crystals display a rich set of mechanisms: Nonlinear deformations, crystal plasticity reminiscent of atomistic mechanisms, shear-induced dilatancy, micro-buckling. Once fully understood and harnessed, we envision that these mechanisms will lead to engineering materials with unusual and attractive combinations of mechanical performances.