It's up for the debate. Some early writers say Christ was crucified with three nails. Others with four nails.
St. Gregory of Tours ("On the Glory of Martyrdom") and St. Cyprian, ("On the Passion" - though this is probably a medieval forgery) say "four nails".
St. Gregory Nazianzus says "three nails" (in his poem "Christus patiens").
To complicate matters, St. Ambrose seems to say that there were only two nails! ("De obitu Theodosii" in P.L., XVI, 1402). According to the Catholic Encyclopedia, other early documents imply that there were only two nails.
I can't figure out why anyone would say "two nails" since Christ had wounds in both hands and in his feet. I can't figure any way for two nails to make four wounds:
See my hands and my feet, that it is I myself; handle me, and see; for a spirit has not flesh and bones as you see that I have. (Luke 24:39)I seem to think three because that is the traditional depiction. Also, I trust Nazianzus better than St. Gregory of Tours and St. Cyprian - especially the statement from the latter is a forgery.
What's your opinion?