Gnosis's Arbitrary Message Bridge (AMB) is a cross-chain messaging system composed of smart contracts and external validators.This system can be used to transfer messages between Gnosis and another external chain in a highly reliable manner.The AMB contract's requireToPassMessage method is used to send a message from an external chain to Gnosis.The method requires the address of the target contract on Gnosis, along with the method to invoke and its parameters.After the message is sent, the AMB emits a UserRequestForAffirmation event, which is monitored by the bridge validators.If 50% of the validators agree, the AMB sends the data to the target contract on Gnosis and invokes the specified method.The AMB solution can be used for simple state transfers as well as more complex token transfer implementations.Gnosis's own OmniBridge token bridge solution is also built on the AMB.Implementing cross-chain messaging can be done with a MessageSender contract on one chain and a MessageReceiver contract on the other.Transferring assets, such as ERC20 tokens, between different chains is a typical example where AMB can be applied.