Question: what was the number of conquistadores in the aztec capital?
About the article "Mexico", section "Conquest (1519)".

Candidate passages:
Tenochtitlan () was the capital of the Aztec empire, which was built on an island in Lake Texcoco in what is now the Federal District in central Mexico.
The city was largely destroyed in the 1520s by Spanish conquistadores.
Mexico City was erected on top of the ruins and, over the ensuing centuries, most of Lake Texcoco has gradually been drained.
Puebla was built because of the need of a Spanish settlement in the route between Mexico City and the port of Veracruz 
La Gran Chichimeca was a term used by the Spanish "conquistadores" of the 16th century to refer to an area of the northern central Mexican "altiplano" (plateau), a territory which today is encompassed by the modern Mexican states of Jalisco, Aguascalientes, Nayarit, Guanajuato and Zacatecas.
They derived the term from the Aztec who referred to the nomadic tribes of the area as “chichimeca”.
The Nahuatl name "Chīchīmēcah" (plural, ; singular "Chīchīmēcatl") means "inhabitants of Chichiman"; the placename Chichiman itself means "Area of Milk".
It is sometimes said to be related to "chichi" "dog", but the i's in "chichi" are short while those in "Chīchīmēcah" are long, a phonemic distinction in Nahuatl.
The word could either have a negative "barbarous" sense, or a positive "noble savage" sense.
Seventy years after the 1521 fall of the Aztec capital, Tenochtitlan (present-day Mexico City), the Spaniards had failed to subdue the north of New Spain, La Gran Chichimeca.
This meant they were unable to exploit the rich silver deposits in the region.
The Spanish, who were unable to defeat the Chichimecas militarily, were forced to make "peace by purchase" by offering them land, farming tools and other goods in exchange for peace.
(See Chichimeca War)During the 1920s and 1930s archaeologists, anthropologists, and cultural geographers began to devise the boundaries of what was thought to be Mesoamerica, the Southwest, and the area between known as the La Gran Chichimeca.
Based upon language groups, iconography, trade items, and re-examinations of Mesoamerican architecture, the boundaries have moved around over the years as a result of new evidence.
Adding to this confusion not all researchers agree the specifics of the boundaries.
However, the participation of the cultures of La Gran Chichimeca in overall Mesoamerican traditions, even if peripherally and occasionally, has led a number of researchers to include the region in the overall Mesoamerican framework. 
Qualpopoca (or Quetzalpopoca) was an Aztec administrator and military commander whose operations on behalf of the Aztec Emperor Moctezuma Xocoyotzin against the Spanish conquistadors at Nauhtla prompted the crisis in Aztec-Spanish relations that provided Hernán Cortés with the pretext he needed to capture Moctezuma and overthrow the Aztec state.
Qualpopoca had killed and captured a number of conquistadors in a battle close to Nauhtla after a dispute about tribute, and thus was the first (and one of the very few) Aztec commanders to have any success against the Spanish.
In revenge, Cortes forced the captive Moctezuma to order his arrest, return him to the Aztec capital Tenochtitlan and subsequently burn him alive in front of the Templo Mayor. 
Spanish conquistadores led by Hernán Cortez conquered the Aztec capital of Tenochtitlan (on the site of present day Mexico City) in 1521, and Franciscan missionaries followed shortly thereafter.
Sahagún was not in this first group of twelve friars, which arrived in New Spain in 1524.
An account, in both Spanish and Nahúatl, of the disputation that these Franciscan friars held in Tenochtitlan soon after their arrival was made by Sahagún in 1564, in order to provide a model for future missionaries.
Thanks to his own academic and religious reputation, Sahagún was recruited in 1529 to join the missionary effort in New Spain.
He would spend the next 61 years there. 
Conquest (1519).
The Spanish conquest of the Aztec Empire began in February 1519 when Hernán Cortés arrived at the port in Veracruz with ca.
500 conquistadores, and later moved on to the Aztec capital.
On his search for gold and other riches, Cortés decided to invade and conquer the Aztec empire.
The ruler of the Aztec empire upon the arrival of the Spaniards was Moctezuma II, who was later killed; his successor and brother Cuitláhuac took control of the Aztec empire, but was among the first to fall from the smallpox epidemic a short time later.
Unintentionally introduced by Spanish conquerors, smallpox ravaged Mesoamerica in the 1520s, killing more than 3 million Aztecs.
Other sources, however, mentioned that the death toll of the Aztecs might have reached up to 15 million (out of a population of less than 30 million).
Severely weakened, the Aztec empire was easily defeated by Cortés and his forces on his second return.
Smallpox was a devastating and selective disease—it generally killed Aztecs but not Spaniards, who as Europeans had already been exposed to it for centuries and were therefore much more immune to it.
The deaths caused by smallpox are believed to have triggered a rapid growth of Christianity in Mexico and the Americas.
At first, the Aztecs believed the epidemic was a punishment from an angry god, but they later accepted their fate and no longer resisted the Spanish rule.
Many of the surviving Aztecs blamed the cause of smallpox to the superiority of the Christian god, which resulted in the acceptance of Catholicism and yielding to the Spanish rule throughout Mexico.
The territory became part of the Spanish Empire under the name of New Spain.
Mexico City was systematically rebuilt by Cortés following the Fall of Tenochtitlan in 1521.
Much of the identity, traditions and architecture of Mexico were created during the colonial period.