First Edition Page from French Patent Application for LEGO DUPLO Brick, 1968

The LEGO DUPLO brick was introduced in 1969, following years of internal development aimed at creating a safer, larger building system for toddlers. This 1968 patent application represents the essential legal foundation for the design, which sought to ensure compatibility between the new, oversized bricks and the traditional, smaller LEGO system bricks. The documentation serves as a critical artifact from a pivotal transition period as the company expanded its target demographic to include the youngest builders.

The design was driven by the need for simplified, tactile geometry that could be safely handled by small children while maintaining the iconic locking clutch power of the original bricks. The patent illustrations capture the utilitarian aesthetic of mid-century industrial design, focusing on the technical specifications of the eight-stud configuration. These early technical drawings are regarded by historians and collectors as the foundational blueprint for a product line that would eventually become a cornerstone of global early-childhood development play.