The settlement layer is the base blockchain that finalizes transactions and provides the trust anchor for higher layers such as bridges, rollups, and application-specific networks. Once a transaction is settled there, other systems treat it as canonical evidence that funds moved, a message was confirmed, or a state change is final.
In cyber security, the settlement layer matters because many cross-chain systems inherit their security from it. Bridges often watch settlement events to decide when to mint, unlock, or release assets on another network. If attackers exploit bridge logic, signer keys, or relayer infrastructure, defenders compare those actions against settlement-layer records to spot unauthorized releases, missing lock events, or suspicious finality assumptions. Strong monitoring of settlement events, confirmations, and reorg risk helps contain fraud and supports incident response when higher layers are abused.