As you enter the church precincts and pass down the walk, try to imagine what life in Mexico was like in the old days. Construction on the church, also known as the Catedral de Asunción de María, began in 1529, a mere 8 years after Cortez conquered Tenochtitlán (Mexico City) from the Aztec, and was completed in 1552. The churchmen could hardly trust their safety to the tenuous allegiance of their new converts, so they built a fortress as a church. The skull and crossbones above the main door are a symbol of the Franciscan order, which had its monastery here. The monastery is open to the public, on the northwest corner of the church property. Also visible on the exterior walls of the main church are inlaid rocks, placed there in memory of the men who lost their lives during its construction.

Once inside, wander through the sanctuaries and the courtyard, and pay special attention to the impressive frescoes painted on the walls, in various states of restoration. The frescoes date from the 1500s and have a distinct Asian style.

The main sanctuary is stark, even severe, with an incongruous modern feeling (it was refurbished in the 1960s). Frescoes on these walls, discovered during the refurbishing, depict the persecution and martyrdom of St. Felipe de Jesús and his companions in Japan. No one is certain who painted them. In the churchyard, you'll see gravestones marking the tombs of the most devout (or wealthiest) parishioners. Being buried on the church grounds was believed to be the most direct route to heaven.