Arnau Mir de Tost

Arnau Mir de Tost (c. 1000 – after 1072) was a Catalan nobleman of Urgell, the lord of Llordà and viscount of Àger, a major figure in the eleventh-century Reconquista in Catalonia. Arnau is sometimes praised as the "El Cid of the Lands of Lleida" for his foundational role in reestablishing Christian rule in the region to the south of Urgell.

Arnau was born at Tost shortly after the year 1000. His father died when he was still young and he became attached to the court of Count Ermengol II. In 1031 he married Arsenda (or Ersenda) and purchased from the count the rights to the castle of Llordà on the frontier with the Caliphate of Córdoba. From his base at Llordà he began a career of conquest in the aftermath of the breakup of the caliphate in numerous petty ṭawā'if. He conquered the Conca Dellà and brought the frontier of Urgell up to the mountainous region of Montsec. His crowning achievement was to seize the mighty qaṣabah (Arabic: قصبة‎‎) of Ajīra (Àger) in 1034, the key fortress in the Andalusi line of defence (the Tagr) against Urgell, which he successfully took by storm twice.

Ermengol promptly enfeoffed Arnau as lord of Àger and charged him with the repopulation of the devastated territory between the Christian and Muslim frontiers. To this end Arnau issued charters specifying the terms of colonisation; Montsec became the centre of a new Christian principality in the south of Urgell. For his primitive chancery Arnau employed an efficient scribe named Vidal, who brought the convenientia (convention) into common practice in western Catalonia, especially through the work he did drawing up conventions on behalf of Raymond IV of Pallars Jussà, the husband of Arnau's daughter Valença. Arnau had extended his influence into Pallars Jussà through this matrimonial alliance (1055), at which time Raymond had pledged him four castles as insurance against his breaking his marriage vows.

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