Between the 12th and 14th centuries the Italian cities, nominally under the fuzzy suzerainty of whichever German Ruler got himself elected Kaiser, ossified into a half-dozen or so distinct independent polities.

So in the 14th-15th century Italian states were wealthy, numerous, and some (The Milanese, the Veronese, and the Florentines) began floating the idea of conquering their neighbors. However, in the 12th century the Italian Cities had only been able to overthrow Emperor Barbarossa after exasperating him over the course of a decade-long whack-a-mole; the cities could barely muster enough men for their own defense. How would one city assemble the manpower to subjugate another?

The answer came in the form of mercenaries.

The first professional soldiers in Italy not tied to the traditional Urban Council ►Vassals of the Urban Councillors arrangement appeared in the thirteenth century after the Crusades, when Germano-Frankish soldiers returning from the Holy Land were occasionally left stranded in Italy. Often little more than roving bandits, they were often rounded up and put to good use during dynastic infighting in Sicily and the south, and eventually lots of them put themselves in positions of serious power (see, "The Other Norman Conquest" by J.J. Norwich).

Subsequent mercenary companies were more often than not veterans of fighting in France and/or Germany, where dynastic fighting had blurred the lines who precisely was fighting against who, and individual vassals and the forces they commanded opportunistically backed different sides based on plunder, risk/reward, and who seemed to be winning. So most early soldiers for hire were mounted men-at-arms; men who had been born into landowning families but perhaps stood to inherit little more than a horse and a name. These men were quick to attach themselves to powerful landed lords, offering their service in battle in exchange for lodgings and a place in the court. Following their lords to war, many stayed behind to plunder and offer (or extort!) their services to whomever could offer them the most.

And the first Italian armed companies were precisely this; for example, the Visconti of Milan in their struggles for supremacy in Milan allied and back-stabbed the landed families of Lombardy in all a manner of combinations. Between 1328 and 1369, Lodrisio Visconti was a particularly popular, powerful, and ruthless member of the family (his personal motto was, "Enemy of god, pity, and mercy") who in spite of having near irrelevant holdings machinated support using external and internal allies (including the powerful Scaligeri of Verona) and one campaigning season called upon as many as six thousand men at arms (we don't know how many men his cousins in Milan raised unfortunately; however Lordoriso lost a key battle at Parabiago in 1339 and suffered heavy casualties, so I'd hazard a guess that the city of Milan with the vassals loyal to his cousin Azzone Visconti could raise just as many men if not more). But rather than serve the highest bidder, these companies were personal armies, not mercenaries for hire; Lordoriso was using Mastino della Scala to usurp his cousin Azzone, as Mastino was using Lordoriso to tear Lombardy apart; no one was "employed" by anyone else. However, these conflicts in Italy set a precedent whereby men willing to fight were loyal to a person, not a state, city, country, or idea.

The recorded company for hire in Italy in the early 14th century was employed first by the Marquis of Monferrat in northwestern Italy (unsurprisingly near France). The Monferrat was threatened on the west by the Counts of Savoy and to the east by the ruthless Visconti of Milan. Apart from calling his knights to arms to repel incursions by both the Milanese and the Savoyards, the Marquis Giovanni also hired the serviced of what amounted to a band of Hundred Years War veterans living as outlaws somewhere in southern France. They were commanded by a German, Alberto Sterz and an Englishman, John Hackwood. They numbered about two thousand men at arms, who rode to battle but "in the english fashion ("all'Inglese") dismounted to fight (probably due to fear of being unable to replace horses should they die). They were probably accompanied by archers armed with longbows.

The later appearance of Italian armed bands for hire can be attributed to a sort of snowball effect. At the late date of 1377, Alberic of Barbiano established the first Italian-only mercenary company. Alberic himself was a son of the Count of Cuneo, a vassal of the Marquis of Monferrat, and was most probably present when his father was called to arms in the conflict between Monferrat and Savoy. Instead of returning home at war's end, Alberic, then sixteen, joined John Hackwood and Alberto Sterz as they traveled south to fight for Pisa, a Tuscan city at war with Florence. At this point (the 1360's) the company, called "The White Company" numbered about four thousand knights and two thousand footmen.

The White Company would go on to be employed by the Republic of Siena, and later the Papacy. When the Pope, in the pocket of the King of France, was convinced to move to Avignon, Hackwood (now sole commander) found himself putting down revolts as cities under Papal control tried to assert their independence. Florence, Milan, and Padua also raised armies and attempted to redraw their borders.

After witnessing Hackwood's forces raze the rebellious city of Cesena to the ground, the aforementioned Alberic left the company. Disgusted by the unchecked antics of foreign mercenaries (as well as with the Papacy, a pawn of foreign powers) Alberic pledged his services to Barbanò Visconti of Milan, rounding up the Italian soldiers in Hackwood's company who would follow him. Alberic's Company of St. George, as they came to be called, would serve as an incubator for many mercenary captains of the next century.

However, this soon created a system by which in the 15th century war became a kind of "Theatre"; campaigns were waged in a (very short) summer campaigning season, and war became a game of figures and hypothetical rather than actual confrontation: whichever side could hire the most mercenaries usually won, with individual companies regularly switching sides depending on who was paying better, who was winning, or other criteria. In addition, even when armies were within striking distance few actual pitched battles were fought; maneuver and positioning became exponentially more important, as captains tried to keep their companies intact.

When two armies finally gave battle, the encounter was often short and relatively bloodless; as soon as one side worked out an advantage, the "loser" often attempted to swiftly withdraw in good order (often to the frustration of their employers; "They avoid defeat just as long as they avoid battle" wrote Macchiavelli).

Sieges were more common, especially early in the century. Between the 13th and 15th centuries, the Milanese, Paduans, Veronese and Florentines were almost continuously involved in some kind low-level warfare, often bullying smaller surrounding towns into submitting in order to establish a ring of fortified burghs around their capital. Oftentimes, these sieges were perpetuated by the mercenaries themselves, who needed to be occupied lest they start pillaging; perpetuating a vicious cycle by which larger, richer cities were constantly hounding out weaker ones.

Equally important was the use of diplomacy coupled with the threat of war, as thanks in great part due to the precarious nature of the Italian Lords' rule over their states, in Central Italy especially states like Pisa, Florence, Siena, Modena and Bologna were nominally Republics, and should the members ruling councils detect that the fortunes of the dominant family were waning they could easily oust them and concede defeat without a fight (in Northern Italy, on the other hand, the Italian states were more susceptible to irreplaceable strongmen).

This all changed when, at the turn of the 16th century, Charles the VIII pursued a claim to the throne of Milan. With real soldiers. Who stood to fight real battles. The Italians and their mercenaries were completely unprepared. This set off the Italian wars, whereby the fate of the Italian States would from then on be decided outside the Peninsula.

Were these "Mercenary Companies" in any way comparable to Napoleon's Grande Armée? Absolutely not, the population of Milan (the largest city in Italy) in this time period was about 100'000 people, count in another 100'000 in the Lombard Countryside, and even arming every man, woman, and child you still have less than a third of the manpower of Napoleon's Grande Armée. What we can do is compare the Italian armies of the time against the armies of other European states, and we have a convenient example: the Battle of Fornovo in the First Italian War pitted the Crown of France against the Republic of Venice, the Duchy of Milan, and the Duchy of Mantua. The Italian army was composed of around eight thousand footmen of mostly Eastern Lombard/Western Venetian extraction, some two thousand knights, and two thousand Stradiotti (light cavalry raised from Venetian colonies). Three fourths of the men were raised in Venetian territory. The French had about eight thousand men, probably equally divided between french knights and Swiss pikemen (plus artillery). This was half of the King of France's army, the other half having been left behind in Naples to pacify the eponymous kingdom (and a small deployment had stayed behind Asti). Three Italian states raised an army more of less comparable to half that of France; not bad (however, the quality of troops, discipline, and getting soldiers to actually fight without regard to plunder is another story altogether, which the Italians never got down).