Philip III, Count of Nassau-Weilburg (20 September 1504 at Neuweilnau Castle in Weilrod – 4 October 1559 in Weilburg) was a Count of the Nassau-Weilburg. Among his major achievements were the introduction of the Reformation, the foundation of the Gymnasium Philippinum in Weilburg and the start of the construction of Schloss Weilburg.
Philip was the son of Louis I of Nassau-Weilburg (1473–1523). After his father's death, he took over the business of government at the age of 19 years.
During Philip's reign, the Nassau-Weilburg part of the County of Nassau consisted of the districts of Weilburg, Merenberg, Usingen, Sonnenberg and Gleiberg. Important towns were Kirberg, Weilmünster and Neuweilnau. Moreover, he held shares in jointly owned territories. Co-owners of those territories included the Counts of Nassau-Saarbrücken and Nassau-Wiesbaden and the Landgrave of Hesse.
The Reformation began during Philip's time in office. Philip promoted the Reformation in his territory, and to this end, he joined forces with Landgrave Philip I of Hesse. On the other hand, he made sure he would not become a vassal of Hesse. He therefore emphasized his position as an immediate count and was active in the Wetterau Association of imperial counts.
Philip died in 1559 in Weilburg, at the age of 55. He was buried in the chapel of Weilburg Castle. He left a heavily indebted county. His goals had exceeded his financial possibilities. His sons Albert and Philip IV ruled Nassau-Weilburg jointly until 1561, and then divided their inheritance, with Albert receiving Weilburg and Philip IV receiving Neuweilnau.
Because his father had left a huge debt, John Louis of Nassau-Saarbrücken was appointed as Philip's guardian and regent of Nassau-Weilburg. Philip took up government himself in 1524. He began by dividing the Lordships of Stauf, Eisenberg and Kirchheim; these were jointly owned by Nassau-Weilburg and Nassau-Saarbrücken. He also renewed the inheritance treaty between Nassau-Weilburg and Nassau-Saarbrücken in 1524. With the progress of the Reformation, the two counts drifted apart and Philip sought support in the Wetterau Association of Imperial Counts.
During the Diet at Regensburg in 1532, Philip of Nassau-Weilburg and his cousin Philip of Nassau-Wiesbaden promised Emperor Charles V 16 knights and 80 foot soldiers, for the ongoing war against the Ottoman Empire. In return, Nassau-Weilburg received market rights for Rückershausen and Usingen.
After the Wetterau Association of Imperial Counts had been dissolved in 1535, Philip approached Landgrave Philip of Hesse. On 25 January 1536, Philip and Philip concluded a comprehensive territory exchange agreement. Nassau-Weilburg transferred the tax revenue of the imperial free city of Wetzlar, the sovereignty over Kalsmunt Castle, the imperial bailiwick of Wetzlar and the dominion over Altenberg Abbey to Hesse. In exchange, he received the castle and city of Katzenelnbogen, the district and castle of Löhnberg and the right to redeem the Hessian share in the castle and district of Hadamar.
On the recommendation of Philip I of Hesse, Philip III formally joined the Schmalkaldic League on 26 August 1537. However, he only supported the League reluctantly. In particular, he did not pay the special contribution that the League had agreed to. His argument was that he had not received a copy of the League's charter.
After Philip I married bigamously in 1540 and the League failed to support him against Trier, Philip III distanced himself from the Schmalkaldic League, without officially terminating his membership. He remained, however, in close contact with Philip I of Hesse.
During the Schmalkaldic War, Philip III supported Philip I with eight knights. After the initial successes of the imperial troops on the Danube, he recalled this support. The imperial field marshal Reinhard of Solms then mediated a reconciliation between Philip III and Emperor Charles V.
After he had ceased his support for the Schmalkaldic League, Philip III worked to recreate the Wetterau Association. The Association was re-established in 1542 and 1549, he was elected chairman of the Association.
To improve his financial situation, Philip tried to intensify mining in his county. Between 1524 and 1530, he founded several iron mines around Weilmünster, together with civil partners. His family managed, over time, to gain the majority of the shares in the mining companies. In 1536 Philip issued a uniform mining regulations for his entire territory. However, the economic recovery he had hoped for, failed to materialize.
Philip initiated several construction projects in his county. The most important project was the construction of a new residence in Weilburg. Schloss Weilburg was built in two phases. Architect Nicholas Schickedanz from Frankfurt built the east wing, a prestigious residential building. Balthasar Wolff from Heilbronn added the south and west wings, which were used as commercial buildings. The construction lasted from 1533 to 1549. Even today, the alliance coat of arms of Philip III of Nassau-Weilburg and Amalie of Isenburg-Büdingen is attached to the stair tower of the east wing.
The dilapidated town church of Weilburg was repaired and a new tower was added in 1555. This tower also served temporarily a water tower. It was also later incorporated into Schloss Weilburg. Below the schloss, a stone bridge across the Lahn was built in 1555, connecting the dominions of Weilburg and Merenberg.
After the construction at Weilburg had completed, Usingen Castle was again expanded between 1551 and 1558.
The Reformation was introduced in Nassau-Weilburg during Philip's reign. Initially he went along with the Wetterau Association of Imperial Counts. However, from 1526, he increasingly took the lead. The Reformation was rapidly implemented in the areas Philip III held jointly with Philip I of Hesse, such as the Hüttenberg district and the area along the river Lahn, with the towns Heuchelheim, Kinzenbach, Launsbach, Wißmar, Rodheim and Fellingshausen.
Philip attended the meeting of the Wetterau Association on 20 June 1524. The meeting decided not to use the Edict of Worms. This brought Philip into conflict with Archbishop Richard of Trier, who held that Philip was interfering in his spiritual jurisdiction and kept back taxes Richard was entitled to.