The Royal Castle in Warsaw was a seat of the Sejm and Senate of the first Rzeczpospolita and also an official residence of the monarchs in Warsaw. It contained the offices of a number of political institutions, arranged around a central courtyard.

The castle is a symbol of Polish statehood and history. Its origins date back almost seven centuries and the design of its present structure has evolved in stages since the fourteenth century. (The actual structure is a mid-20th-century reconstruction of the original castle, which was mostly demolished by German occupiers during World War II.)

Castle in the Middle Ages

In the 1339 the Papal Legate in Warsaw heard a case brought by the King of Poland, Kazimierz the Great, against the German Teutonic Order. He claimed that they had illegally seized a slice of Polish territory — Pomerania and the Kujawy region. The documents in this case are the earliest written testimony to the existence of Warsaw. At that time a fortified town surrounded by earthen and wooden ramparts, and situated where the Royal Castle now stands, it was the seat of Trojden, Duke of Masovia. At the end of the 13th century, during the Duke's Conrad II of Mazovia reign, the wooden-earthen gord called Smaller Manor () was built. The next duke, Casimir I, decided to build the first brick building here at the burg-city's area the Great Tower ().

In the middle of the 14th century the Castle Tower, whose structure up to the first storey has survived to this day, was built, while during the reign over Masovia by Duke Janusz I the Elder, the Curia Maior (Big Manor) was erected between 1407 and 1410. Its facade, which was still standing in 1944, was knocked down by the Germans, but has been rebuilt since then. The character of the new residence and its size (47.5 m/14.5 m) decided the change of the buildings status, and from 1414 it functioned as a Prince Manor.

Renaissance

When the Masovia region was incorporated in the Kingdom of Poland in 1526, the edifice, which until then had been the Castle of the Dukes of Masovia, became one of the royal residences. From 1548 onwards Queen Bona Sforza resided in it with her daughters Izabela, who became Queen of Hungary, Catherine, later to become Queen of Sweden, and Anna Jagiellon, later Queen of Poland. In 1556–1557 and in 1564 the King of Poland, Zygmunt August, convened royal parliaments in Warsaw. They met in the Castle. Following the Lublin Union (1569), by which the Polish Crown and the Grand Duchy of Lithuania - were united as a single country, Warsaw Castle was regularly the place where the parliament of the Two-Nations State met. In 1569–1572 King Zygmunt August started alterations in the Castle, the architects being Giovanni Battista di Quadro and Giacopo Pario.

The Curia Maior was altered so as provide a meeting place for the Parliament, with premises for the Chamber of Deputies (Sejm - delegates of the gentry) on the ground floor (the Old Chamber of Deputies), and the Senate Chamber (where the Senators debated in the presence of the King) on the first floor. This was one of the first attempts in Europe to create a building that would be used solely for parliamentary purposes. The parliamentary character of the Curia Maior is stressed by the paintings of the facade — the coats-of-arms of Poland, of Lithuania, and of the various regions from which the delegates were elected. A new Renaissance—style building, known as the "Royal House", was erected next to the Curia Maior. The king resided there when the parliament was in session.

The Vasas Era and the Deluge

The next alterations to the Castle were made in the reign of Sigismund III, who transferred the royal residence from Kraków to Warsaw. In 1598–1619 the Castle was enlarged. Giovanni Trevano was in charge of the reconstruction. His plans were probably amended by the Venetian architect Vincenzo Scamozzi.

Between 1601–1603 Giacomo Rodondo finished the new northern wing. From 1602 Paolo del Corte was doing stonework. Later after 1614, when Matteo Castelli took the lead, the western wing was built (from today's Plac Zamkowy side) as chancelleries and a marshals office. The southern wing was built at the end. In that way five-wings in a mannerist-early baroque style were built. In 1619 the New Royal Tower () also called Sigismund's Tower was finished. It was 60 meters high and was placed in the middle of a newly built west castle 90 meters in length. At the top of the tower, a clock with gilded hands and copper face was placed. The new tower's spire was 13 meters high and had glided knobs and a copper flag at the top.

On 29 October 1611 in the Senator's Chamber, Tsar Vasili IV of Russia, who had been captured by the hetman Stanisław Żółkiewski, paid homage to the Polish king Sigismund III Vasa.

The Polish king Sigismund III and his successors of the Vasa dynasty — Władysław IV Vasa and John II Casimir Vasa — collected many rich works of art in the castle, such as oriental fabrics, tapestries, and numerous paintings by such famous artists as Titian, Veronese, Jacopo, Leandro Bassano, Tintoretto, Palma il Giovane, Antonio Vassilacchi, Tommaso Dolabella, Guercino, Guido Reni, Joseph Heintz, Bartholomeus Spranger, Roelant Savery, Rembrandt, Pieter Soutman, Peter Danckerts de Rij, Peter Paul Rubens, Jan Brueghel the Elder, Daniel Seghers, Georg Daniel Schultz and sculptures by Giambologna, Giovanni Francesco Susini and Adriaen de Vries. These splendid works of art were either destroyed or plundered during the invasions of Poland by Sweden and Germans of Brandenburg during (The Deluge, in 1655–1657). The Swedes and Germans took all the priceless pictures, furniture, tapestries, the royal library, the crown archive, numerous sculptures, whole floors and royal flags. In the castle they had a military Lazareth field hospital, which additionally contributed to the devastation of the buildings. A few months later armies destroyed the rest, plundering most of the copper elements and tearing up the rest of castle's floor.

The majority of the preserved castle furnishings from the Vasa period found its place in the collection of the Visitationist Monastery in Warsaw as donations from the last Vasa, John II Casimir and his wife Marie Louise Gonzaga.

In 1628 the first Polish opera – Galatea, was staged at the Castle. The great opera hall (double-storied, over 50m long), which existed at the Royal Castle, was demolished by Swedes and Germans and rebuilt in the 1660s by King Jan Kazimierz.

Late Baroque period

In 1657 the reconstruction of the castle started, under the Italian architect Izydor Affait's guidance. Because of the lack of money the following Polish king, Michał Korybut Wiśniowiecki did not decide on radical rebuilding, just limiting himself to rebuilding destroyed buildings. Because of bad conditions of the residence he had to move to Ujazdów Castle in 1669. Until 1696 when the next Polish king, John III Sobieski died, no serious works were done. They only limited work to current inspections of the building's condition. Sessions of Parliament continued to be held in the castle, as well as various State occasions, such as when the Hohenzollern Dukes of Prussia paid homage to the Kings of Poland and occasions when the king received the ambassadors of foreign countries.

After choosing Augustus II in an election in 1697, the castle again began to deteriorate. A new conflict with the King of Sweden, Charles XII significantly limited the king's budget. Despite problems, in 1698 Augustus II commissioned a residence reconstruction project. In 1700 it was done by Johann Friedrich Karcher, who came from abroad. On 25 May 1702 the Swedes re-seized the Royal Castle in Warsaw, creating a hospital with 500 beds, and into The Chamber of Deputies and ministers’ rooms, they placed a stable. During the Polish army's siege in 1704 the castle was retaken. However, it was soon retaken once more by Sweden's army. In 1707, by virtue of the peace treaty between Augustus II and Charles XII of Sweden, Russian allied troops entered Warsaw, and Tsar Peter I of Russia settled in the castle. After two months, Russian forces were removed from Warsaw, taking with them works of art from the castle, including Tommaso Dolabella's pictures, which included two that were very important for Russians: The Defense of Smolensk and Russian Tsar Vasili IV compelled to kneel before Polish King Sigismund III of Poland. The Władysław's Opera Hall was completely devastated and was never restored.

The reconstruction according to Karcher's plans began from 1713 to 1715. In 1717 the Parliament Hall was completely rebuilt. It was used to serve the Saxon rulers as a coronation hall. During the following years, between 1722 and 1723, the other castle halls were converted-under the direction of architect Joachim Daniel von Jauch, the new Senate Chamber was built, and all the furnishings moved from the old to the new location, including among others: 60 Polish provincial emblems, paneling, mouldings and lizens. On 31 May 1732, a fire broke out in the castle destroying the west elevation and part of the Zygmunt's Tower and the exterior façade sculptures, known as armature.

The next reconstruction project of the Royal Castle appeared after Augustus III took to the Polish throne in 1733. New plans, which were formed in 1734 and developed in 1737 by architect Gaetano Chiaveri, saw among other things, the reconstruction of the castle's façade on the Vistula side in the rococo style, which was meant to form a new so called Saxon elevation and also the conversion of the north-east part with the Altana Tower, where it was planned for 3 two-storey rysalits to be built on. The reconstruction work according to these plans was carried out with various intensity between 1740 and 1752. During the period of 1740-1747 the façade on the Vistula side was reconstructed in the late baroque style (architects: Gaetano Chiaveri, Carl Friedrich Pöppelmann, Jan Krzysztof Knöffel). One of the best sculptors who did work on the castle in this period was Jan Jerzy Plersch, who made the royal decorative frames, mouldings and statues called the Famous Figures, which held the royal crowns on the top of the middle rysalit, of the Saxon elevation, on the Vistula side. The last reconstruction work of this period was finished by late 1763, after the death of Augustus III, when Plersch made the last sculptures and frames with province emblems for the Parliament Hall.

The Stanisław August period

The most splendid period in the history of the Castle was during the rule of Stanisław August Poniatowski (1764–1795). This monarch collected exquisite works of art, many of which have survived to this day. He recruited first-rate architects such as Jakub Fontana, Merlini, Kamsetzer, and Kubicki, to work on the castle, as well as splendid painters such as Marcello Bacciarelli, Bernardo Bellotto (otherwise known as Canaletto), Franciszek Smuglewicz, Kazimierz Wojniakowski, and Jean-Baptiste Pillement and eminent sculptors such as André le Brun and Jakub Monaldi, and famous French artists such as the architect Victor Louis. The total reconstruction of the castle planned by the king did not come to fruition, but the interior was changed to the neoclassical style - although this, known in Poland as the Stanisław August style, was rather different from neo—classicism in the rest of Europe.