Outline of Biblical Usage 1) a bringing together, gathering (as of fruits), a contracting
2) in the NT, an assembling together of men, an assembly of men
3) a synagogue
a) an assembly of Jews formally gathered together to offer prayers and listen to the reading and expositions of the scriptures; assemblies of that sort were held every sabbath and feast day, after wards also on the second and fifth days of every week; name transferred to an assembly of Christians formally gathered together for religious purposes
b) the buildings where those solemn Jewish assemblies are held. Synagogues seem to date their origin from the Babylonian exile. In the times of Jesus and the apostles every town, not only in Palestine, but also among the Gentiles if it contained a considerable number of Jewish inhabitants, had at least one synagogue, the larger towns several or even many. These were also used for trials and inflicting punishment.
Because the synagogue system was begun when the Jews went into captivity in Babylon. Until then they were allowed to worship in their own temple. Upon the return to Israel, they rebuilt the temple, but they were still used to having meeting in the synagogues. Also sects had come up with different ideas about how to best practice their faith and so it was natural to keep the synagogue system in place.
answer: It was the Temple. When the temple was destroyed in 70 C.E. the religion moved inside homes but the desire to gather and worship together, to study and celebrate together was strong and synagogues were formed wherever the Jews were scattered (or with the ones that remained in the area).
Because during Th time of the Old Testament, thee was a temple or had recently been a Temple, therefore, there were very few synagogues and certainly none in their current form.
In the Old Testament, its was called a Temple, House of God, or a Tabernacle,
Synagogues usually have a large hall for prayer (the main sanctuary), smaller rooms for study and sometimes a social hall and offices. Some have a separate room for Torah study, called the Beth mid rash ?("House of Study").