Adam Clarke on 1 Corinthians 15:6

Above five hundred brethren at once - This was probably in Galilee, where our Lord had many disciples. See Mat 28:16. What a remarkable testimony is this to the truth of our Lord's resurrection! Five hundred persons saw him at one time; the greater part of whom were alive when the apostle wrote, and he might have been confronted by many if he had dared to assert a falsity.