Unlike the plague of 1596–1602, which claimed 600,000 to 700,000 lives, or a little under 8% of the population and initially struck northern and central Spain and Andalusia in the south, the Great Plague, which may have arisen in Algeria, struck the Mediterranean side of Spain first. The coastal city of Valencia was the first city to be hit, losing an estimated 30,000 people. The disease raged through Andalucía, in addition to sweeping the north into Catalonia and Aragon. The coast of Málaga lost upwards of 50,000 people. In Seville, quarantine measures were evaded, ignored, unproposed and/or unenforced. Unsurprisingly, the result was horrific. The city of Seville and its rural districts were thought to have lost 150,000 people—starting with a total population of 600,000. Altogether Spain was thought to have lost 500,000 people, out of a population of slightly fewer than 10,000,000, or nearly 5% of its entire population. This was the greatest, but not the only, plague of 17th century Spain.
Not quite twenty-five years later, Spain found itself once again in the grips of a furious plague. For nine years (1676–1685), ebbing and flowing like a great wave, it ravaged all Spain. It struck with especial virulence in the areas of Andalucía and Valencia. The poor harvest of 1682-83 brought with it famine conditions which weakened the exhausted population even further. This last plague of the 17th century, plus the famine that followed in its wake, is estimated to have taken an additional 250,000 lives.
Three great plagues ravaged Spain in the 17th century. They were:
Factoring in normal births, deaths, plus emigration, historians reckon the total cost in human lives due to these plagues throughout Spain, throughout the entire 17th century, to be a minimum of nearly 1.25 million. As a result, the population of Spain scarcely budged between the years 1596 and 1696.
The disease is generally believed to have been bubonic plague, an infection by the bacterium Yersinia pestis, transmitted via a rat vector. Other symptom patterns of the bubonic plague, such as septicemic plague and pneumonic plague were also present.