The Ankh Cross is a looped Tau Cross and an ancient Egyptian hieroglyph meaning life. In ancient Egyptian, sandal thong and life had the same pronunciation (hmophony). Deciding on a hieroglyph for sandal thong was relatively easy. But deciding on something for the less tangible life, was a challenge. So they used the hieroglyph that had the same sound. For many civilisations using this symbol, the loop represented the sun. The loop is also a perfect symbol that has neither beginning nor end, so it represents the eternal soul. The symbol also represents the Tree of Life, with its trunk and foliage.
Early Christians adopted this symbol because of its resemblance to the cross. In particular, it was adopted by the Coptic Church of Egypt.