Because the Hope was referred to as an "anchor," the anchor was the earliest known Christian symbol. It was used to represent the Hope of resurrection unto everlasting life. At Pompeii, the Roman city buried by lava in 79 AD when Mt. Vesuvius erupted, a ring was discovered with a beautiful image of an anchor and the Greek word elpis, "hope," inscribed on it.
Some of the earliest Christian graves have an anchor carved into the rock next to them.
Christians today use a cross as their common symbol, but there is no reference to the cross being a revered Christian image until after the Roman Empire became Christian. The cross was so abhorred as an instrument of torture that no early Christians venerated it. Historically, the first interest in the image of the cross came after Queen Helena, the mother of the Roman Emperor Constantine, reportedly found the "true cross" on her trip to Israel in 326 AD.
Before that time, the anchor was the symbol that the early Christians used to show their hope of resurrection and a wonderful, everlasting future.