This technical report describes "Project Sid," an experiment that aims to create and study AI civilizations within a Minecraft environment. The researchers introduce a new cognitive architecture called PIANO, designed to enable agents to interact with each other and their environment in real-time while maintaining coherence across multiple output streams. They show that agents using PIANO can make significant individual progress by acquiring Minecraft items and that they can form meaningful relationships in large groups, demonstrating social understanding. Additionally, they explore the concept of civilizational progress through benchmarks that measure agent specialization into distinct professions, adherence to collective rules, and cultural transmission through memes and religion. The report concludes by discussing limitations of the current system and outlining areas for future research.