Here is the story of the arrival of St. Francis at the Porziuncola (1):
When this church too was at length finished he [Saint Francis] came unto the place that is called The Little Portion wherein a church had been reared in days of old in honor of the most Blessed Virgin, Mother of God, but which was then deserted and cared for by none. When the man of God beheld it thus abandoned, by reason of the ardent devotion that he had toward the Sovereign Lady of the world, he took up his abode there, that he might diligently labor to repair it. Perceiving that Angels oft times visited it - according unto the name of that church, that from old time was called Saint Mary of the Angels - he abode there by reason of his reverence for the Angels, and his especial love for the Mother of Christ.
This place the holy man loved before all other places in the world; for here he began in humility, here he made progress in virtue, here he ended in happiness, and, dying, commended it unto the Brethren as a place most beloved of the Virgin.
Concerning this place a certain devout Brother, before his conversion, beheld a vision right worthy to be recounted. He beheld a countless host of men stricken with blindness, with their faces uplifted unto heaven, on bended knees, encircling this church, and they all, stretching out their hands on high, cried unto God with tears, beseeching His mercy and light. And lo, there came a great radiance from heaven, illumining all, and this gave light unto each one of them, and granted the longed-for salvation. This is the place wherein the Order of Brothers Minor was begun by Saint Francis according unto the impulse of the divine revelation.
Saint Bonaventure, Life of Saint Francis of Assisi, chapter 2
(1) Porziuncola, also called Portiuncula (in Latin) is a small Catholic church located within the Papal Basilica of Saint Mary of the Angels in Assisi. It is the place from where the Franciscan movement started.