The strategic importance of the site was increased by the fact that it lay on a major river estuary, where vessels could dock at the port of Suso.

By ancient tradition, Basques, and indeed other peoples in Medieval Europe, held assemblies under a tree, usually an oak, to discuss matters affecting the community.

The laws of Biscay continued to be drawn up under this tree until 1876, with each town and village in the province sending two representatives to the sessions, known as General Assemblies.

This early form of democracy was recorded by the philosopher Rousseau, by the poet William Wordsworth, by the dramatist Tirso de Molina and by the composer Iparragirre, who wrote the piece called Gernikako Arbola ("The Tree of Gernika" in Basque).

The oath of King Ferdinand, known as the "Catholic Monarch", on June 30, 1476, is depicted in a painting by Francisco de Mendieta [es] popularly known as "El besamanos" ("The Royal audience").

Day-to-day life comprised agriculture (growing of cereals, vegetable and fruit), crafts (menders, tailors, cobblers, flax manufacturers) and trade (transportation and sale of goods and produce).

[citation needed] On April 26, 1937, during the Spanish Civil War, Guernica was the scene of a massive aerial bombing attack by the Condor Legion of Nazi Germany's Luftwaffe and the Italian Aviazione Legionaria.

It has inspired musical compositions by Octavio Vazquez (Gernika piano trio), René-Louis Baron, Lenny White,[8] and Mike Batt (performed by Katie Melua),[9] and poems by Paul Eluard (Victory of Guernica), and Uys Krige (Nag van die Fascistiese Bomwerpers; English translation from the Afrikaans: Night of the Fascist Bombers).

As part of these celebrations, a statue of Count Tello, made by local sculptor Agustín Herranz, was set up in the Fueros Square.

On April 26, 1937, during the Spanish Civil War, the town was razed to the ground by German aircraft belonging to the Condor Legion, sent by Hitler to support Franco's troops.

As part of the "Symbol for Peace" movement, Gernika has twinned with several towns, including Berga (Catalonia – 1986), Pforzheim (Germany – 1988) and Boise, Idaho (United States – 1993).

A combination of both local languages (Castillian and Basque) into a single sentence, this translates roughly as "not a stroke of work gets done on Mondays".

They came not just to buy or sell at the produce market, but also to eat at the town's renowned restaurants and afterwards perhaps to watch a pelota game at the local court.

The bombing of Guernica by Nazi Germany's Luftwaffe and the Italian Aviazione Legionaria was deliberately chosen to occur on a Monday (April 26, 1937), because it was known that the Basque people who lived outside of Guernica proper would travel into town for the Market Day, thus affording the pilots of the German and Italian aircraft the opportunity to murder as many people as possible.