On 11 September this year, I watched as Barcelona was submerged in a lake of Catalonia's colours - red and yellow.
For almost all of the rest of the world, that date is now inextricably associated with the downing of the World Trade Centre's Twin Towers in New York and the attack on the Pentagon.
But for Catalans those events in 2001 appear to take second place to La Diada, the region's national day, which commemorates the final fall of Barcelona in 1714 following a siege by Castilian and French forces that had lasted over a year.
This year, a white star on a blue background augmented many of the red and yellow "senyeras", as the Catalans call their flag. The star identifies its bearer as a supporter of full-scale independence from the kingdom of Spain and, this year, it was as though there were an entire galaxy on display.
There is no doubt in my mind that the dramatic surge in secessionist sentiment in Catalonia is closely related to the eurozone crisis.
As the wealthiest part of Spain, Catalonia makes the largest extra contribution to the budget for distribution around the poorer parts of the country.
The finance ministry in Madrid estimates this could be as high as 17.8bn euros (£14.3bn; $22.9bn), or more than 8% of Catalonia's GDP.
This system, which has generated much resentment among Catalans, was almost identical to the argument I heard frequently in Slovenia and Croatia during the late 1980s in the run-up to the collapse of the former Yugoslavia.
"Why," the Slovenes and Croats argued, "should we have to subsidise poor areas like Kosovo and Macedonia?"
In Spain, however, Catalan resentment has been exacerbated in recent times by the swingeing budget cuts made by Mariano Rajoy's government in Madrid as it implements tough austerity measures demanded by the European Union.
Catalan nationalists criticise cuts to their social services while they continue to underwrite the poorer regions.
Fuel for nationalism
But, above all, secessionists point to history. The 11 September emerged as the National Day not only for the heroism of Rafael Casanova, Barcelona's mayor at the time of the siege, but because of what happened after the city's surrender.
Within two years, the victorious Spanish king, Philip V, punished the territories of Aragon by issuing the Nueva Planta decrees.
Catalonia had joined Aragon in the 12th Century but had always maintained its own parliament.
Philip V abolished Barcelona's Cortes and imposed Castilian law on all parts of Aragon's crown, including the Catalans.
In doing this, he was following the pattern of several large European states who were busy centralising government and economic management. And, although the Spanish empire was clearly not the power it had been in the 16th Century under Philip II, her monarchs continued expanding territorially until it reached its greatest extent at the end of the 18th Century.
But the quashing of autonomous Catalan institutions that had existed for many centuries provided some powerful fuel for Catalan nationalism over the next 300 years.
In the 20th Century alone, the Spanish government has restored Catalan autonomy thrice and abolished it twice.
When economic and political strains have increased, the calls for secession have typically become louder and the most traumatic event in recent history, the Spanish Civil War, evokes especially bitter memories among Catalans.
Not only did the victory of the fascist dictator, General Francisco Franco, result in the brutal repression of those who fought against him on the Republican side but it also resulted in Madrid again ordering the abolition of Catalonia's autonomous institutions.
Spain of many parts
During Franco's 40 years in power, the dictator never forgave the Catalans their resistance during the Civil War and his policies systematically neglected the region, especially with regard to its economic infrastructure.
The Catalans had rarely felt themselves part of an entity called Spain, in part because throughout modern history, the idea of a Spanish nation state has been amorphous. The core of today's Spain first came together as a political entity in 1469 when the marriage of Isabella and Ferdinand united the two houses of Castile and Aragon.
But their various territories boasted different traditions and political cultures. Catalonia was a key maritime power that was linked into networks across the Mediterranean, looking east. Its commercial pre-eminence was then undermined by two critical events which both fostered resentment and led to a decline in Catalonia's influence.
The first was the discovery of the New World and the decision to give the port of Seville in the south exclusive rights to all the goods, notably silver, imported from the vast resources opening up in South America. The whole focus of early modern Spain's economic policy shifted away from Barcelona.
The second was Philip II's decision to move his court from Toledo to Madrid in 1561. This small town in the middle of an arid, barren region but right in the middle of Philip's Hispanic territories soon became the critical political hub not just of the peninsula but the rapidly expanding Spanish Empire. Flaunting its new found wealth and undoubted military power, Spain was feared in Europe and beyond.
Still, nobody within Iberia - except Philip and his courtiers - recognised this country as "Spain". For Catalans, Aragonese, Galicians and Basques, it was an amalgam of which Castile, the imperial centre, was just one part.
That does not mean, however, that the Catalan push for independence has always enjoyed the support it does currently. For Catalonia has also benefited from the association with Spain and its economy is now highly integrated with the rest of the country.
Furthermore, the population is by no means exclusively Catalan, especially in Barcelona.
Many workers from other regions in the country have sought work there and then settled.
According to the most recent census, just under 50% of the city's inhabitants read and write the language fluently while another 25% can converse or at the very least understand it with few difficulties.
But of course almost everyone in the city speaks and writes Spanish. And those immigrants are decidedly nervous at the prospect of Catalan independence.
After the death of General Franco, it took Spain's delicate democracy just under a decade before it was safe from a fascist restoration.
Under the reign of King Juan Carlos, a cautious monarch sensitive to regional stresses in Spain, Barcelona and Madrid appeared to have reached an understanding as to how they could live together.
Essentially, Catalonia has enjoyed wide-ranging autonomy again since the late 1970s.
But this time, it is an external event - the eurozone crisis - and its impact on Spain, already suffering a major banking crisis, that has brought relations between Madrid and Barcelona close to breaking point.
Misha Glenny's radio series on Spanish history, The Invention of Spain, is available on the BBC iPlayer