Benedictine abbey located on the outskirts of the village of Anserall, main capital of Les Valls de Valira (Alt Urgell), about 300 m N of this village, at right of Valira River, three kilometres in the road from La Seu d'Urgell to Andorra; closed on 1592.
The origin of this monastery is Visigothic and Episcopal. Historical data known are from the end of the eighth century, on the occasion of the adoptionist heresy devised by Fèlix (or Feliu), the monastery abbot (also Bishop of Urgell) and supported by Bishop Elipand of Toledo, Primate of the Visigothic Church.Nonetheless, the origins of this monastery are not very clear since the monks have falsified documents in different occasions, in order to obtain papal profits. Amongst these falsified documents in Sant Serni is a false bull issued by Leo III. Fèlix, Tavèrnoles abbot and also bishop of Urgell was once persecuted and deposed by Charlemagne.
In 815 this monastery received several donations from the counts of Urgell and Cerdanya and are founded the monasteries of Sant Salvador de la Vedella (in the Berguedà County) and Sant Pere de Casserres. In 1019, became under their tutelage the monastery of Sant Llorenç de Morunys with the appointment of the abbot to both monasteries. In his time of splendour, in the eleventh century, the monastery's possessions were extended from Andorra to Berguedà through Pallars Jussà and Cerdanya counties. They owned also possessions in Castile and Aragon.
On January 17th, 1040, a new church was consecrated by the bishops Eribau of Urgell and Arnulf of Ribagorça. It was dedicated in honour of the Virgin and the saints Michel and Sadurní. Guillem was the abbot then and in the consecration ceremony were invited several personalities of the time as the counts of Urgell, the archbishops of Narbonne and Arles, and the bishsops of Elna, Béziers, Girona and Toulouse of Lengadòc. In the consecration document are also detailed the possessions referred to the benedictine order leaded by the monks.
In 1099, Pope Urban II gave the monastery bull immunity. The splendour of Sant Serni lasted until the end of the thirteenth century. Its last abbot (commendatory) was Onofre Ferrer who died in 1584. Although the monastery continued active without abbot, with a congregation of two monks, it was finally secularized and closed by order of Pope Clement VIII in 1592.Monastery rents were reverted to the seminary in La Seu d'Urgell; meanwhile in the monastery was settled a perpetual vicarage.
Set of apses restored SST, 1979; JMNT photo