The two Bishops of Aleppo went missing in April 2013.
On 22nd April 2013 Bishop Yohanna Ibrahim of the Syrian Orthodox Church and Bishop Boulos Yaziji of the Greek Orthodox Church were stopped by armed militants while travelling north of Aleppo.
The men were abducted and their driver was killed, it is thought that a fourth Christian who was travelling with the group was able to escape.
The group had been travelling to an area near the border with Turkey to take part in negotiations for the release of two priests that had been abducted in February 2013.
The whereabouts of the bishops and priests are still not known.
To mark the anniversary and encourage prayer the Syrian Orthodox and Greek Orthodox Patriarchs of Antioch issued a joint statement appealing to the international community.
It describe the plight of the bishops as "a miniature of the great human suffering" inflicted on Syria.
It reads: If the intention of the kidnapping event to intimidate us, however, we, Christians, are the descendants of those who, two thousand years ago, put on the name of Christ in this particular land.
"We are no giants, and we do not have the support of the "giants." We mould our bread from this land, and from the strength of our belonging to it. Thus, we preserve our identity as Antiochian Easterners, through whatever difficulties or tribulations.
"We have spared no effort, but our main and only hope is in God.
"Our strength is only and solely acquired from the determination of our people who are deeply rooted in, and hold great love for, their Church and their land. We shall continue to live in this East, ringing our bells, building our churches, and lifting up our Crosses."
They reject the notions that Christians should be considered as a "minority" and that Christians can be protected emigrating, saying Syrian Christians share the pain and uncertainty of persecuted believers all over the world.
The Patriarchs' appeal comes as the latest round of peace talks in Geneva is taking place.
Syrian Christians request prayer that "violence will cease, peace will be restored and the clear rule of law will be applied equally for all in every part of Syria and that all who remain abducted will know the Lord's strength and sustaining, and that they will be released soon."
