|Source: Lourens & Lucassen 1997, pp. 112–114|
Leiden was formed on an artificial hill (today called the Burcht van Leiden) at the confluence of the rivers Oude and Nieuwe Rijn (Old and New Rhine). In the oldest reference to this, from circa 860, the settlement was called Leithon. The name is said to be from Germanic *leitha- "canal"  in dative pluralis, thus meaning "at the canals". "Canal" is actually not the completely proper word. A leitha (later "lede") was a human-modified natural river, partly natural, partly artificial.
Leiden has in the past erroneously been associated with the Roman outpost Lugdunum Batavorum. This particular castellum was thought to be located at the Burcht of Leiden, and the city's name was thought to be derived from the Latin name Lugdunum. However the castellum was in fact closer to the town of Katwijk, whereas the Roman settlement near modern-day Leiden was called Matilo.
The landlord of Leiden, situated in a stronghold on the hill (motte), was initially subject to the Bishop of Utrecht but around 1100 the burgraves became subject to the county of Holland. This county got its name in 1101 from a domain near the stronghold: Holtland or Holland.
Leiden was sacked in 1047 by Emperor Henry III. Early 13th century, Ada, Countess of Holland took refuge here when she was fighting in a civil war against her uncle, William I, Count of Holland. He besieged the stronghold and captured Ada.
Leiden received city rights in 1266. In 1389, its population had grown to about 4,000 persons.
Siege of 1420
In 1420, during the Hook and Cod wars, Duke John III of Bavaria along with his army marched from Gouda in the direction of Leiden in order to conquer the city since Leiden did not pay the new Count of Holland Jacqueline, Countess of Hainaut, his niece and only daughter of Count William VI of Holland.
Burgrave Filips of Wassenaar and the other local noblemen of the Hook faction assumed that the duke would besiege Leiden first and send small units out to conquer the surrounding citadels. But John of Bavaria chose to attack the citadels first.
He rolled the cannons along with his army but one which was too heavy went by ship. By firing at the walls and gates with iron balls the citadels fell one by one. Within a week John of Bavaria conquered the castles of Poelgeest, Ter Does, Hoichmade, de Zijl, ter Waerd, Warmond and de Paddenpoel.
On 24 June the army appeared before the walls of Leiden. On 17 August 1420, after a two-month siege the city surrendered to John of Bavaria. The burgrave Filips of Wassenaar was stripped of his offices and rights and lived out his last years in captivity.
16th to 18th centuries
Relief of Leiden
(1574), painting by Otto van Veen
. Inundated meadows allow the Dutch fleet access to the Spanish infantry positions.
17th-century houses along the Herengracht
Townhall and bridge (de Koornbrug)
The 1852 Sijthoff
printing office, Leiden
Leiden's west gate, the Morspoort
at night, showing the chimney of the Light Factory
Leiden flourished in the 16th and 17th century. At the close of the 15th century the weaving establishments (mainly broadcloth) of Leiden were very important, and after the expulsion of the Spaniards Leiden cloth, Leiden baize and Leiden camlet were familiar terms. In the same period, Leiden developed an important printing and publishing industry. The influential printer Christoffel Plantijn lived there at one time. One of his pupils was Lodewijk Elzevir (1547–1617), who established the largest bookshop and printing works in Leiden, a business continued by his descendants through 1712 and the name subsequently adopted (in a variant spelling) by contemporary publisher Elsevier.
In 1572, the city sided with the Dutch revolt against Spanish rule and played an important role in the Eighty Years' War. Besieged from May until October 1574 by the Spanish, Leiden was relieved by the cutting of the dikes, thus enabling ships to carry provisions to the inhabitants of the flooded town. As a reward for the heroic defence of the previous year, the University of Leiden was founded by William I of Orange in 1575. Yearly on 3 October, the end of the siege is still celebrated in Leiden. Tradition tells that the citizens were offered the choice between a university and a certain exemption from taxes and chose the university. The siege is notable also for being the first instance in Europe of the issuance of paper money, with paper taken from prayer books being stamped using coin dies when silver ran out.
Leiden is also known as the place where the Pilgrims (as well as some of the first settlers of New Amsterdam) lived (and operated a printing press) for a time in the early 17th century before their departure to Massachusetts and New Amsterdam in the New World.
In the 17th century, Leiden prospered, in part because of the impetus to the textile industry by refugees from Flanders. While the city had lost about a third of its 15,000 citizens during the siege of 1574, it quickly recovered to 45,000 inhabitants in 1622, and may have come near to 70,000 circa 1670. During the Dutch Golden Era, Leiden was the second largest city of Holland, after Amsterdam. Particularly due to the work by Herman Boerhaave (1668–1738), it played a crucial role in the establishment of modern chemistry and medicine.
From the late 17th century onwards Leiden slumped, mainly due to the decline of the cloth industries. In the beginning of the 19th century the baize manufacture was altogether given up, although industry remained central to Leiden economy. This decline is painted vividly by the fall in population. The population of Leiden had sunk to 30,000 between 1796 and 1811, and in 1904 was 56,044.
From the 17th to the early 19th century, Leiden was the publishing place of one of the most important contemporary journals, , known also as Gazette de Leyde.
19th and 20th centuries
On 12 January 1807, a catastrophe struck the city when a boat loaded with 17,400 kilograms (38,360 pounds) of gunpowder blew up in the middle of Leiden. 151 persons were killed, over 2,000 were injured and some 220 homes were destroyed. King Louis Bonaparte personally visited the city to provide assistance to the victims. Although located in the centre of the city, the area destroyed remained empty for many years. In 1886 the space was turned into a public park, the Van der Werff park.
In 1842, the railroad from Leiden to Haarlem was inaugurated and one year later the railway to Den Haag was completed, resulting in some social and economic improvement. Perhaps the most important piece of Dutch history contributed by Leiden was the Constitution of the Netherlands. Johan Rudolf Thorbecke (1798–1872) wrote the Dutch Constitution in April 1848 in his house at Garenmarkt 9 in Leiden.
Leiden's reputation as the "city of books" continued through the 19th century with the establishment of publishing dynasties by Evert Jan Brill and Albertus Willem Sijthoff. Sijthoff, who rose to prominence in the trade of translated books, wrote a letter in 1899 to Queen Wilhelmina regarding his opposition to becoming a signatory to the Berne Convention for the Protection of Literary and Artistic Works. He felt that international copyright restrictions would stifle the Dutch publishing industry.
Leiden grew 12-fold in size between 1896 and 1981, annexing land from neighboring municipalities
Leiden began to expand beyond its 17th-century moats around 1896 and the number of citizens surpassed 50,000 in 1900. After 1920, new industries were established in the city, such as the canning and metal industries. During World War II, Leiden was hit hard by Allied bombardments. The areas surrounding the railway station and Marewijk were almost completely destroyed.
The city's biggest and most popular annual festival is celebrated at 3 October and is called simply 3 Oktober. The people of Leiden celebrate the end of the Spanish siege of 1574. It typically takes place over the course of two to three days (usually two but three if there's a Sunday involved) and includes parades, a hutspot feast, historical reenactments, a funfair and other events. The city has recently started to host the Leiden International Film Festival, the fastest growing festival of its type in the Netherlands.
Leiden has important functions as a shopping and trade centre for communities around the city. The University of Leiden is famous for its many discoveries including Snells law (by Willebrord Snellius),
the famous Leyden jar, a capacitor made from a glass jar, invented in Leiden by Pieter van Musschenbroek in 1746. Another development was in cryogenics: Heike Kamerlingh Onnes (1913 Nobel prize winner in physics) liquefied helium for the first time (1908) and later managed to reach a temperature of less than one degree above the absolute minimum. Albert Einstein also spent some time at Leiden University during his early to middle career.
The city also houses the Eurotransplant, the international organization responsible for the mediation and allocation of organ donation procedures in Austria, Belgium, Croatia, Germany, Luxembourg, the Netherlands and Slovenia. Leiden also houses the headquarters of Airbus, a global pan-European aerospace and defence corporation and a leading defence and military contractor worldwide. The group includes Airbus, the leading manufacturer of commercial aircraft worldwide.