frederick i (holy roman empire), called frederick barbarossa (1123?-90), holy roman emperor and king of germany (1152-90), king of italy (1155-90), and as frederick iii, duke of swabia (1147-52, 1167-68). he was born in waiblingen, the son of frederick ii of hohenstaufen, duke of swabia, and the nephew of conrad iii, king of germany. conrad iii, favoring frederick over his own son, on his deathbed recommended to the german princes that frederick be chosen for the german kingship and the imperial throne. accordingly, after the death of his uncle in 1152, frederick barbarossa was made german king and elected holy roman emperor. he conceived of his imperial title as a grant from god, through the german princes, and wished to restore the glory of the roman empire.

he consequently decided to consolidate the imperial position in germany and italy and began by issuing a general order for peace among the princes of germany, at the same time granting them extensive concessions. in 1154 he proceeded to italy, where he received the lombard crown at pavia. the following year he was crowned holy roman emperor by pope adrian iv, whose authority frederick had reinstated before his coronation. in 1156 pope adrian aroused frederick against the papacy by implying in a letter to him that the emperor held lands only as a fief from the pope. two years later frederick incurred the hostility of the lombards by demanding recognition of all his royal rights, including his power to appoint the imperial podesta, or governor, in every town. such cities as milan, piacenza, brescia, and cremona considered that demand a denial of their communal liberties and in 1158 began a struggle that lasted until 1183 and required frederick to lead five expeditions to italy.

between 1158 and 1162 frederick warred with milan and its allies, subduing that city and confirming claims to other italian cities. meanwhile frederick had set up a series of antipopes in opposition to the reigning pope, alexander iii, who espoused the cause of the milanese and their allies and who, in 1165, excommunicated frederick. by attacking the leonine city in rome in 1167-68, frederick was able to install one of the antipopes, paschal iii, on the papal throne. the lombard league, consisting of the cities of milan, parma, padua (padova), verona, piacenza, bologna, cremona, mantua (mantova), bergamo, and brescia, was formed in 1167 and eventually acknowledged pope alexander as leader.

during the next seven years the league acquired military strength, rebuilt milan, constructed the fortress city of alessandria, and organized a federal system of administration. the fifth expedition (1174-76) of frederick to italy terminated in defeat by the lombard league at legnano. the defeat was significant in military history, because it was the first major triumph of infantry over a mounted army of feudal knights. frederick was forced in 1177 to acknowledge alexander iii as pope and in 1183 to sign the peace of constance, acceding to the demands of the lombards for autonomy but retaining imperial suzerainty over the towns. although imperial control in italy was virtually ended by his defeat at legnano, frederick managed to enhance his prestige in central europe. he made poland tributary to the empire, raised bohemia to the rank of a kingdom, and erected the margravate of austria into an independent hereditary duchy. his own power as emperor in germany was firmly established in 1180, when he ended his long struggle with the welfs by putting down a revolt led by the welf henry the lion and depriving him of most of his lands. frederick initiated the third crusade in 1189, and in the next year, having resigned the government of the empire to his son henry, later holy roman emperor henry vi, set out for asia minor. after gaining two great victories over the muslims at philomelion (now aksehir) and iconium (now konya), he was drowned in the calycadnus (now göksu) river in cilicia (now in turkey) on june 10, 1190.