"We have this hope, a sure and steadfast anchor of the soul, a hope that enters the inner shrine behind the curtain, where Jesus, a forerunner on our behalf, has entered, having become a high priest forever according to the order of Melchizedek." Hebrews 6:19-20
The anchor is an ancient Christian symbol. For the early Christians, who lived during the Roman persecution, the anchor was a symbol of safety. The verse from Hebrews is the first written connection of hope with the symbol of the anchor. Persecuted Christians also used the anchor symbol as a means to "hide" the cross.
However important the anchor was, the fish was even more so. Its popularity among Christians was due principally to the famous acrostic consisting of the initial letters of five Greek words forming the word for fish (Ichthus), which words briefly but clearly described the character of Christ and the claim to worship of believers: "Ἰησοῦς Χριστὸς Θεοῦ Υἱὸς Σωτήρ", meaning, Jesus Christ, Son of God, Saviour. Greeks, Romans, and many other pagans used the fish symbol before Christians. Hence the fish attracted little suspicion, making it a perfect secret symbol for persecuted believers. When threatened by Romans in the first centuries after Christ, Christians used the fish to mark meeting places and tombs, or to distinguish friends from foes.
The fish has remained a prominent Christian symbol. In addition to the meaning of Ichthus, it also ties us to the story of Jesus feeding the multitudes with 5 loaves and 2 fish.
The anchor is not as common, but still a powerful symbol of the steadfast love of God and our safety in Him.