Paris (The Merge)Happened on September 15th, 2022The Paris upgrade was triggered by the proof-of-work blockchain passing a terminal total difficulty of 58750000000000000000000. This happened at block 15537393 on 15th September 2022, triggering the Paris upgrade the next block. Paris was The Merge transition - its major feature was switching off the proof-of-work mining algorithm and associated consensus logic and switching on proof-of-stake instead. Paris itself was an upgrade to the execution clients (equivalent to Bellatrix on the consensus layer) that enabled them to take instruction from their connected consensus clients. This required a new set of internal API methods, collectively known as the Engine API, to be activated. This was arguably the most significant upgrade in Ethereum history since Homestead!
