B'day of the Church

Yesterday was the feast of the Pentecost and so the birthday of the Church. It makes a lot of sense to really celebrate this relatively relegated occasion. To consider the Holy Spirit as the founding member of the Church is quite logical and a deeper study of the Church itself will find this foundation most appropriate. However I wonder where and when on earth did the structure which is the so-called 'church' in normal understanding originate? Perhaps with Constantine and his decision to convert to Christianity. Given the fact that this formal organised structure of the 'church' is more known and 'adhered to', it is appropriate that the Spiritual foundations of the Church are recognised and occasions like these are solemnised.