The 4th Regiment of Line Infantry (Polish: 4. pułk piechoty liniowej) was a military unit of the Kingdom of Poland. Formed in 1815, the regiment distinguished itself in the battles of the November Uprising and remains one of the best-known units of the Polish Army of the epoch. The soldiers of the regiment are collectively known in Polish historiography as Czwartacy.
The regiment was not related to earlier 4th Regiment of Front Guard (established in 1733). However, it was a direct descendant of the Napoleonic-era 4th Infantry Regiment of the Duchy of Warsaw. Despite the fact that in 1812 Napoleon lost control over Poland, the regiment remained loyal to the emperor and fought in, among others, the bloody Battle of Leipzig and the Battle of Arcis-sur-Aube, the penultimate battle of Napoleon Bonaparte. After his abdication and exile to the Elbe, the remnants of the regiment returned to Russian-controlled Poland with their banners and flags, swore an oath to the Russian tsars and formed the core of a newly created infantry regiment. The regimental banner is preserved in the Warsaw-based Museum of the Polish Army.
Officially named the "4th Regiment of Line Infantry", the soldiers of the new unit inherited the nickname of Czwartacy, roughly translated as "Those of the Fourth", under which both the Napoleonic and the new unit was best known. Like its predecessor, the new regiment was based in Warsaw and its main barracks was located in the Sapieha Palace. The regiment was composed of a mixture of people roughly reflecting the wide social spectrum of contemporary Warsaw: it include both the Szlachta, or Polish gentry, and the burghers, but also a large number of serfs and peasants.
Because of the proximity of the barracks to the palace of Grand Duke Constantine Pavlovich of Russia, the 4th Regiment became one of his favoured military units and its soldiers enjoyed the status of his personal guard. In practice this often meant that the Grand Duke, very fond of his military units, but also very cruel and brutal in their treatment, was very keen on marching the soldiers of the regiment days and nights, regardless of the weather. The morale in the maltreated regiment was low, yet any sign of discontent was brutally repressed: among the people to be the most repressed was Major Walerian Łukasiński. Denounced as the founder of a secret society, he was sentenced to seven years of imprisonment, but eventually was held for 46 years in Russian prisons, most of the term in solitary confinement and without a trial.
Following the outbreak of the November Uprising, the regiment rebelled against the Russian tsars along with most of the army of the Kingdom of Poland. It fought from the very first day of the uprising and distinguished itself in the First and Second Battle of Wawer, as well as the battles of Dębe Wielkie, Ostrołęka and the final Battle of Warsaw. During the war the regiment received 214 Virtuti Militari crosses: five 3rd class, 55 fourth class and 154 fifth class. This made it one of the most highly decorated Polish units of the epoch. During the uprising the unit also was often referred to as "Tysiąc Walecznych" ("A Thousand Brave Men") both by the press and general populace. This nickname was popularised in Europe by a German poet Julius Mosen, who published in 1832 a popular poem idealising the regiment and its actions during the war of 1830-1831.