While agricultural taxes extracted labor from both sexes, mit'a service was a draft levied annually on all able-bodied males. Mit'a service lasted for various lengths of time and embraced a wide range of activities from working on construction projects to participating in military campaigns. As long as some males remained at home to attend fields, the state was free to determine the numbers of draftees to be mobilized and their length of service. With millions of male subjects to draw upon, mit'a gave Tahuantinsuyu a very labor intensive economy. This has vivid archaeological expressions in tens of thousands of kilometers of well-built road networks, vast irrigation and terrace systems, and great architectural monuments. The splendor of Cuzco, which so amazed the conquistadores, was impressive testimony to the toil of multitudes rendering mit'a. Thirty thousand men are said to have labored at one time simply building Sacsahuaman, the fort of Cyclopean masonry dominating the imperial capital.
It profits a government to expend the
returns from one tax in a manner that will expand the returns from another.
Revenue expansion among Andean states entailed transforming labor, an ephemeral
item, into a productive commodity with tangible yields. To this end the
Inca and earlier states invested mit'a labor in the acquisition of more
agricultural land, which could then be taxed and yields stored in qollqa,
thereby augmenting the imperial coffers. This strategy was pursued through
both conquest and reclamation of formerly unfarmed land. Over many millennia
reclaiming land required ever greater efforts, undertaken by progressively
larger senorios and states that could mobilize mit'a from multiple communities.
Beginning with Pukara and culminating in Cuzco, the major political centers
of Andean civilization all organized large reclamation 
projects in their
adjacent hinterlands. This work is dramatically expressed in the multitudes
of masonry terraces surrounding Cuzco and lining the Urubamba Valley in
its descent to Machu Picchu. The Inca not only resculpted their imperial heartland,
but they also opened lands in other quarters of the empire, moving entire
communities, known as mitamaq colonies, to work on newly claimed
lands.
Using mit'a conscripts to acquire new land through conquest made Tahuantinsuyu the largest nation of the hemisphere. The Inca maintained a professional officer core drawn from Cuzco's royal families, but it is not clear to what degree they maintained standing armies. Resistance to Inca expansion was often from fortified hilltop bastions called pakaras, whose high walls and dry moats were costly to take by storm. Attackers suffered far greater losses than defenders. Yet pukaras were completely vulnerable to long-term siege and the Inca were victorious because they could field forces for the many months needed to starve out defenders. Repeated use of siege tactics suggests that some imperial legions were comprised of standing forces.
