Our Lady of Sorrows (Mater Dolorosa, Beata Maria Virgo Perdolens) is a devotional title of the Blessed Virgin Mary honoring her as the Mother who stood beside the Cross of her Son. The devotion draws together the Seven Sorrows of Mary: (1) the Prophecy of Simeon (Luke 2:34-35); (2) the Flight into Egypt (Matt 2:13-14); (3) the Loss of the Child Jesus in the Temple (Luke 2:41-52); (4) Mary meeting Jesus on the way to Calvary; (5) the Crucifixion (John 19:25-27); (6) the Body taken down from the Cross; (7) the Burial of Jesus.
The Servite Order (Order of Servants of Mary), founded in Florence in 1233 by the Seven Holy Founders, spread the devotion through the Rosary of the Seven Sorrows, the Servite Rosary of seven decades. A Servite feast of the Compassion of Mary was granted in 1423; Benedict XIII extended it to the universal Church in 1727; Pius X transferred it to September 15 in 1913, the day after the Exaltation of the Holy Cross.
The Stabat Mater — the 13th-century Latin hymn traditionally attributed to Jacopone da Todi, the Franciscan poet — is the sequence of the feast: "Stabat Mater dolorosa / iuxta crucem lacrimosa / dum pendebat Filius."
The apparition at La Salette (September 19, 1846) — where the Virgin appeared weeping — is iconographically a Mater Dolorosa apparition, and the calendar closeness to the September 15 feast has long been devotionally noted.
Sources
Our Lady of Sorrows — Wikipedia.
Pilgrimage Sites Dedicated to Our Lady of Sorrows
La Salette
France · Europe
La Salette is a major Catholic pilgrimage site where the Virgin Mary appeared to two children in 1846, bringing a message of reconciliation and conversion.
Rome
Italy · Europe
Rome holds the tombs of Peter and Paul, the four papal basilicas, the Holy Stairs and the catacombs of the early Church.
Seville
Spain · Europe
Seville's magnificent Cathedral houses the tomb of Saint Ferdinand III and draws pilgrims during Holy Week processions.
Maria Taferl
Austria · Europe
Lower Austria's second-largest Marian shrine, where a miraculous crucifix and Pietà have drawn pilgrims since 1633.
Maria Dreieichen
Austria · Europe
Twin-towered basilica on the Manhartsberg ridge where pilgrims venerate the Sorrowful Mother at a miraculous oak since 1656.
Maria Luggau
Austria · Europe
Carinthia's only basilica, where a peasant woman's 1513 vision led to one of Austria's great Servite pilgrimage shrines in the Lesachtal Alps.