Nowadays the Cross is an almost exclusively Christian symbol. So it may come as a surprise to realise that it was used in pre-Christian times in many societies to represent a wide variety of themes. For the ancient Assyrians it represented their Sky God, Anu.
In the early 16th century, when Cortes arrived in South America, he and his Spanish countrymen were mystified by the number of crosses found in the local (pagan) temples. The only reason they could think of was that the cross had been introduced by the disciple, St Thomas, traditionally regarded as the Apostle of the Indies. They just couldn't imagine that these crosses were anything other than Christian in origin.
In fact these South American crosses were associated with their gods Tlaloc and Quetzalcoatl.
In Egypt, the Ankh, nowadays associated with the Christian Coptic Church in the country, was originally the property of the ancient Egyptian gods, symbolising immortality.
Food for thought, eh 
prydwen
thanks.
If truth be told Christ was most probably crucified on a 'T' bar which was more common to the Romans. The original symbol of Christianity was of course the fish or Icthus
The first appearance of a cross in Christian art is on a Vatican sarcophagus from the mid-5th Century. It was a Greek cross with equal-length arms. The first crucifixion scenes didn't appear in Christian art until the 7th century CE.