The Church of Santa Maria Assunta became a parish church in the 15th century and was consecrated in 1644. The exterior shows a very simple form with the harmonious geometry of the Tuscan style. The façade features an elegant portal surmounted by two windows and an oeil-de-boeuf with a fresco. The monumental organ enclosed in a wooden case gilded in pure gold dates from the 17th century. Following the transfer of St. Valentine’s relics in 1699, the building was decorated with fine paintings. The interior reveals a rococo decoration, with a beautiful painted wooden ceiling.
It houses the Museum of Sacred Art, includeing a large number of sacred furniture in noble metal from 16th to 19th century. The Museum contains noteworthy works of art, part of the treasure of the parish church, mostly composed of candlesticks, chalices , reliquaries produced by famous Tuscan silversmiths in the 17th and 18th centuries . The furnishings , in large part, were donated to the Pieve after the arrival in Bientina of the relics of St. Valentine. The museum offers a valuable display of liturgical vestments, dating from 16th to 18th century , of considerable interest for the value and refinement of the fabrics.