This is a complex question with no single, universally agreed-upon answer. The reason is that "Christianity" itself evolved over time, and the concept of a distinct "religion" wasn't always as clear-cut as it is today. Here's a breakdown of the different perspectives:
* Early Christianity: All Christian denominations trace their roots back to the teachings and ministry of Jesus Christ in the 1st century AD and the subsequent spread of those teachings by his apostles. So, in a very broad sense, *all* forms of Christianity are connected to that original, earliest movement.
* The Undivided Church: Many historians and theologians would point to the period before the Great Schism of 1054 as the era of the "Undivided Church." This church, though diverse in its practices and local traditions, was united in fundamental doctrines. The closest modern-day descendants of this "Undivided Church" are often considered to be the Eastern Orthodox Church and the Catholic Church.
* Eastern Orthodox Church: The Eastern Orthodox Church maintains that it has preserved the original teachings and practices of the early Church more faithfully than any other denomination. They trace their lineage back to the original apostles and the patriarchates of Constantinople, Alexandria, Antioch, and Jerusalem.
* Catholic Church: The Catholic Church also claims to be the original Christian Church, founded by Jesus Christ and led by the apostles, with the Pope as the successor of St. Peter.
* Other Considerations:
* Some scholars argue that certain Eastern churches, such as the Armenian Apostolic Church or the Syriac Orthodox Church, have maintained traditions that predate some of the developments in both the Catholic and Eastern Orthodox Churches. However, these churches also experienced their own evolutions and distinct developments.
* It's important to remember that early Christianity was not monolithic. There were diverse interpretations of Jesus's teachings and variations in practices from region to region.
In summary:
While all Christian denominations share a common origin in the teachings of Jesus, the Eastern Orthodox Church and the Catholic Church are often considered the oldest continuous Christian traditions, tracing their roots back to the early Church before the major schisms. However, other Eastern churches also have strong claims to preserving very ancient traditions. It ultimately depends on how you define "oldest" and what criteria you use to evaluate continuity and faithfulness to the earliest forms of Christianity.