The Paschal Hymn

Technically known as the Paschal Troparion (a kind of Byzantine hymn), written by St. John of Damascus (aka Damascene), the shortest of Orthodox hymns, sung over and over between Pascha and Ascension Thursday:

Christ is risen from the dead, trampling down death by death, and upon those in the tombs bestowing life!

Or in Old Church Slavonic:

Khristos voskrese iz mertvih, smertiu smert poprav, i sushchim vo grobeh zhivot darovav!

Or in Greek (probably Koine, I think):

Christos anesti ek nekron, thanato thanaton patisas, ke tis en tis mnimasi zoin harisamenos!

For many musical settings and many more languages, see here.