Madius (died after 1358) was a prelate of the Catholic Church who served as the bishop of Duvno from between 1298 and 1311 to his resignation in 1344. Konrad Eubel considers him a second bishop of Duvno, while Dominik Mandić left the question open whether Madius was indeed the second or the first bishop of Duvno, as he couldn't find any document confirming his alleged predecessor John of Hoio as the bishop of Duvno. During his episcopate, he was involved in long-lasting litigations against the archbishops of Split as a representative of Bishop Valentin of Makarska over the control of Omiš and other church objects. Madius resigned due to what he calls "maliciousness of the people", which might refer to the opposition of his faithful to pay taxes and the political plight which befell him after his patrons from the Šubić family lost the political influence after the conquest of their domains by Stephen II, Ban of Bosnia. He nevertheless retained the title of a bishop and, according to Ante Škegro, lived on the territory of the Archdiocese of Split.
The first complete written biography of Madius is the one authored by Dominik Mandić. Bishop Madius is mentioned for the first time on 3 January 1337 in a document of the Trogir city council, where he participated as a witness. He was mentioned a second time in a charter of the Split church archive from 1344, where he was mentioned as a participant of the Split church council at which he represented the interests of the bishop of Makarska Valentin who was in dispute with the archbishop of Split Dominik Luccari and his successor Hugolin Brancao over Omiš. The dispute, which also involved Roman Curia, produced three long-lasting judicial proceedings (1342 - 47; 1352 - 56; 1365).
As the bull on the Madius' appointment hasn't been found, the exact year of the beginning of his episcopate remains unknown. If he was the first bishop of Duvno, as Valentin was the first bishop of Makarska, Škregro argues that the start of his episcopate could be placed between 1298 and 1311. Madius states that he served as a bishop for many years and had to resign his office due to the "maliciousness of the people". Some authors consider that the "maliciousness" refers to the opposition of the people to the church taxation, while others state that the term referred to the political difficulties that befell him after the demise of the Šubić family. By the time of his and Valentin's resignation, a significant number of the Vlach population, which wasn't sympathetic to authority, nor political or ecclesiastical, arrived on the territory of their dioceses. The Vlachs were especially sensitive to taxation and were ready to change their denomination. However, Škergo argues that wider political implications must be considered when examining Madius' and Valentin's resignations, considering that their dioceses were under the patronage of the Šubić family. After Stephen II, Ban of Bosnia conquered the territories of their dioceses, he considered the two bishops to be the sympathisers of the Šubićs, while at the same time, the Catholic Church lost its political bedrock and became susceptible to the influence of the heterodox Bosnian Church. After Stephen II's conquest, the two bishops lost the significance they enjoyed under the Šubićs'. Stephen II conquered the Diocese of Duvno before the Diocese of Makarska, of which the majority of the territory was under Stephen II's rule by 1326. This enabled the protuberance of the Bosnian Church there as well.
With the demise of the Šubićs, the two bishops lost the support of their hierarch, the archbishop of Split, whose territory had to be taken under pressure from the Šubićs for these two dioceses to be established. The two bishops were also involved in legal disputes against the archbishops of Split since 1342, with Valentin claiming control over Omiš and other church objects with support from Madius.
In 1344, Madius travelled to Avignon, the residing place of the pontiff at the time, to resign from his post. The Pope appointed John de Leoncello as his successor in 1345. Madius, nevertheless, retained the right to the episcopal title. He was mentioned as a bishop after his resignation on 20 February 1346. Škegro suggests that after his resignation, Madius moved somewhere on the territory of the Archdiocese of Split to assist Valentin in his litigations against the archdiocese. On 25 August 1358, Madius was elected by the Split city council as a member of the delegation that was tasked with negotiating with the representatives of King Louis I of Croatia and Hungary after Split was retaken from the Republic of Venice.
Various authors have doubts about whether Madius was a Benedictine monk from the nearby Sustjepan monastery (Ivan Ostojić) or a Franciscan (Marijan Žugaj and Damir Karbić). The counts of Bribir from the Šubić family who founded the Diocese of Duvno and the Diocese of Makarska were sympathisers and patrons of the Franciscans and raised their churches and friaries. Thus, for example, Paul I Šubić established at least two Franciscan friaries, that of Saint Mary in Bribir and of Saint John in Skradin.