Actually it is possible. According to wikipedia the city, according to a 2006 estimate, has 1,528,683 habitants. The entire department, again according to the wikipedia article, had 2,433,602 people living in the department in the year 2005. Due to a great wave of internal migration, my personal and unscientific guess is that the population has increased by at least 250,000, although obviously I can not corroborate this. However, this so called "march" was given the name of "Cabildo del Millon" because supposedly a million people attended. Although in the Spanish version of Wikipedia, there is an article which mentions that an estimate was made of 902,000 people present in this march in favor of autonomy and against the government led by Evo Morales.