Good question! It seems that "divorce" and "remarriage" as understood by the Orthodox does trace back their roots to the 4th century with st. Basil the Great
"A man who marries after another man’s wife has been taken away from him will be charged with adultery in the case of the first woman; but in the case of the second he will be guiltless" (Second Canonical Letter to Amphilochius 199:37 [A.D. 375]).
Here are the Canons of St. Basil: http://www.ccel.org/ccel/schaff/npnf214.xvii.xi.html
They that marry a second time, used to be under penance a year or two. They that marry a third time, three or four years. But we have a custom, that he who marries a third time be under penance five years, not by canon, but tradition. Half of this time they are to be hearers, afterwards Co-standers; but to abstain from the communion of the Good Thing, when they have shewed some fruit of repentance.
However, officially allowing for remarriage did not happen in East until the 8th century. Removing the penalty of lengthy excommunication for those contracting a second marriage, is much more recent, in 19th century.
As a separate note, Orthodox canon law can permit a second and even a third marriage, but strictly forbids a fourth. In theory divorce is only recognized in the case of adultery, but in practise is also recognised in light of other reasons.
Here is a list of reasons for divorce in the Russian Orthodox Church:http://eadiocese.org/Court/en.reasonsdissolution.htm
The Holy Council of the Russian Orthodox Church of 1917-18 recognized as being legitimate the following reasons for dissolution of a marriage sanctified by the Church:
- apostasy from Orthodoxy
- adultery and unnatural vices
- incapacity for marital cohabitation
- affliction by leprosy or syphilis
- unknown absence
- jail sentence with deprivation of rights
- infringement upon the life and health of spouse and children
- incest or prostitution of spouse
- entering into a new marriage
- serious, incurable mental illness
- intentional desertion