A cross is a wooden structure used in ancient times by the Romans to execute people, often by nailing or tying them to it until they died. This is called "crucifixion." Crucifixion was a painful and shameful form of execution, typically used to kill the worst criminals, slaves, or rebels. Jesus was crucified on a cross even though he was innocent (Matthew 27:32–56).
Jesus told his followers they must “take up their cross” to follow him (Matthew 16:24). This means being willing to face hardship and suffering for the sake of faith.