 The first church built on the cathedral site also had a tabernacle , but its exact location is unknown . During the construction of the cathedral , the tabernacle was housed in what are now the Chapels of San Isidro and Our Lady of Agony of Granada . However , in the 18th century , it was decided to build a structure that was separate , but still connected , to the main cathedral . It is constructed of tezontle ( a reddish porous volcanic rock ) and white stone in the shape of a Greek cross with its southern facade faces the Zócalo . It is connected to the main cathedral via the Chapel of San Isidro . 
 The first church built on the cathedral site also had a tabernacle , but its exact location <a href='drop_aux' title='1'><mark>is</mark></a>unknown . During the construction of the cathedral , the tabernacle was housed in what are now the Chapels of San Isidro and Our Lady of Agony of Granada . However , in the 18th century , it was decided to build a structure <a href='null_relcl' title='2'><mark>that</mark></a>was separate , but still connected , to the main cathedral . It is constructed of tezontle ( a reddish porous volcanic rock ) and white stone in the shape of a Greek cross with its southern facade <a href='uninflect' title='3'><mark>faces</mark></a> the Zócalo . It is connected to the main cathedral via the Chapel of San Isidro . 
The first church built on the cathedral site also had a tabernacle , but its exact location unknown . durin the construction of the cathedral , da tabernacle was housed in wat are now the Chapels of San Isidro and Our Lady of Agony of Granada . However , in the 18th century , it was decided to build a structure was separate , but still connected , to the main cathedral . It is constructed of tezontle ( a reddish porous volcanic rock ) and white stone in the shape of a Greek cross witt its southern facade face the Zócalo . It is connected to the main cathedral via the Chapel of San Isidro .