The Duchy of à »agaà  (, ) or Duchy of Sagan () was one of the duchies of Silesia ruled by the Silesian Piasts. Its capital was à »agaà  in Lower Silesia, the territory stretched to the town of Nowogród Bobrzaà Âski in the north and reached the Lusatian Neisse at Przewóz in the west, including two villages beyond the river (Pechern and Neudorf).
It was formed in 1274 from the western part of the Duchy of Gà Âogów and existed under Piast rule until 1304, then again from 1322 to 1394 and from 1413 to 1472. Since 1329 it was under the suzerainty of Bohemia; it was acquired by the Saxon House of Wettin in 1472, before it was finally seized by the Bohemian king in 1549.
The à »agaà  ducal title later passed to Bohemian and French nobility, in 1742 it was annexed by Prussia. Re-established as a fief of the Prussian throne in 1844, it formally existed until its official termination in 1935.
After the death of Duke Konrad I of Gà Âogów, his heirs divided his duchy. The castle at à »agaà  became the residence of his youngest son Przemko, the first Duke of à »agaà  from 1278, who established a monastery of Augustinian Canons there. In 1284 he swapped his estates for the Duchy of à Âcinawa and was succeeded by his elder brother Konrad II the Hunchback. When Konrad II died in 1304 all former Gà Âogów estates were re-unified under his surviving brother Henry III.
In 1309 Henry III of Gà Âogów was followed by his eldest son Henry IV the Faithful, who in 1321 divided the duchy again between him and his younger brothers. He ceded Gà Âogów to Przemko II and retired to à »agaà Â, which again became the capital of a duchy in its own right. From 1322 to , Henry IV additionally controlled the eastern part of Lubusz Land with the towns of Torzym and SulÃÂcin, and the MiÃÂdzyrzecz castellany in north-western Greater Poland. In 1329 all sons of Henry III of Gà Âogów became vassals of King John of Bohemia - with the exception of Przemko II who died suddenly two years later. In 1353, the towns of Nowe Miasteczko and Polkowice passed to the Duchy of à »agaà  from the Duchy of à Âcinawa. When in 1393 Henry VI the Elder, grandson of Henry IV died without issue, the estates were again re-unified with Gà Âogów until in 1412 Jan I, the eldest son of Duke Henry VIII the Sparrow became the sole ruler of the à »agaà  duchy. After a fierce battle for the inheritance, in 1472 his son Jan II the Mad finally sold it to the Saxon duke Albert III the Bold with the consent of the Bohemian king Matthias Corvinus, thus ending the centuries-long Piast rule.
The former Augustinian monastery complex in à »agaà  with the church of the Assumption, the main burial site of Piast dukes of à »agaà Â, is designated a Historic Monument of Poland.
Duke Albert III, the progenitor of the Albertine line of the Wettin dynasty, ruled jointly with his elder brother Elector Ernest, even after the partition of the Wettin lands in 1485. With the accession of Albert's son Henry IV in 1539, à »agaà  turned Protestant. The Albertine and Ernestine branches came to a rupture when in the Schmalkaldic War of 1546âÂÂ47 Duke Maurice of Saxony fought against his cousin John Frederick I, who by the Capitulation of Wittenberg had to renounce his claims to à »agaà Â. In 1549 Maurice, now Elector, by an agreement with the Bohemian king Ferdinand I of Habsburg.
As a Bohemian fief, Emperor Ferdinand II of Habsburg in 1627 allotted à »agaà  to Albrecht von Wallenstein, then Duke of Frýdlant, Imperial generalissimo in the Thirty Years' War, who hosted his astrologer Johannes Kepler here. After Wallenstein's assassination it passed to Václav Eusebius Frantià ¡ek, Prince of Lobkowicz and so to the illustrious Bohemian family of Lobkowicz, who had the Baroque à »agaà  Palace erected. King Frederick II of Prussia conquered à »agaà  in the course of the First Silesian War, after which by the 1742 Treaty of Breslau it fell to Prussia.
In 1786 à »agaà  was purchased by Peter von Biron, Duke of Courland, who bequeathed it to his daughter Wilhelmine, from whom in 1842 it passed to her sister Pauline and finally to her sister Dorothea, the divorced wife of Edmond de Talleyrand-Périgord, a nephew of the great French diplomat Talleyrand. Dorothea came to pass her retirement years at à »agaà Â; a patent of King Frederick William IV of Prussia on 6 January 1845 invested her as Duchess of Sagan and Napoleon III recognized the title in France, in favor of her son Napoleon Louis. In France there is a prince and a duc de Sagan. The double title, both Prussian and French, served to render the duc de Sagan a neutral party in World War II: his Château de Valençay provided a safe haven for treasures of the Louvre during the German occupation of France.
The Duchy had a vote on the Silesian County Council, and the holder in the rank of a Duke was a member of the Prussian House of Lords. In 1900 the duchy had an area of and 65,000 inhabitants. After 1815 it was incorporated into the Prussian Province of Silesia, and was part of Landkreis Sprottau from 1932. With the implementation of the Oder-Neisse line in 1945 the à »agaà  territory became again part of Poland, with the exception of the strip of land on the western bank of the Neisse river, which became part of East Germany; today this territory belongs to the German municipality of Krauschwitz.