Charlemagne's capital at Aachen made political, geographical and military sense. Aachen was, firstly, surrounded by lands owned by the Carolingian family already, and placing his capital in this already existing framework created a political power base, reducing the chances of noble or popular insurrection. Secondly, when considering how conducting successful warfare and going on summer campaigns was an intrinsic element of Frankish kingship, Aachen was the perfect mustering point, Charlamagne's Piccadilly Circus; his repeated warfare against the Saxons in modern day Germany between 772-804 meant that Aachen, more North than central as Paris is, became a more significant settlement.

It is worth noting that Paris at this time was not a hugely substantial settlement; urbanisation during this time period was extremely limited, and although Paris was set to become important due to its location on the Seine, it was not so yet. What made a settlement successful or grow was the placement of a royal mint, a successful trading node such as is visible in York or London during this period, the presence of military or the presence of a royal court. These last two were mainly what drove Aachen to success; Charlemagne really only began spending time at Aachen during the last 10 years of his life, but he did begin construction of his palace at Aachen in 794, which brought with it a royal court. The presence of this and it being a military muster point contributed to the local economy in a huge way, attracting merchants, craftsmen and others to the urban centre, resulting in specialisation of labour and an expansion of the economy. In this sense, Charlemagne did not simply choose his capital expecting people to flock to it instantly, however, the economic potential of a royal court and military campaigns during the summer months proved to be all too tempting for many.

Sources: Jong, de Theuws, Van Rhijn. "Topographies of Power in the Early Middle Ages" (2001), and Riché's "Daily Life in the World of Charlemagne" (1978)