The Byzantium Fork was a major upgrade in Ethereum's development roadmap, part of the Metropolis phase. It introduced several Ethereum Improvement Proposals (EIPs), enhancing privacy, security, and scalability. Key updates included the implementation of zk-SNARKs for privacy, reduced block rewards, and changes in gas costs for specific operations. Byzantium also laid the foundation for Ethereum’s transition from proof-of-work to proof-of-stake consensus mechanisms.