Text 13 

tatraika-stham jagat krtsnam
pravibhaktam anekadha
apasyad deva-devasya
sarire pandavas tada 

Translation

At that time Arjuna could see in the universal form of the Lord the unlimited expansions of the universe situated in one place although divided into many, many thousands.

Commentary by Srila Prabhupada 

The word tatra (“there”) is very significant. It indicates that both Arjuna and Krishna were sitting on the chariot when Arjuna saw the universal form. Others on the battlefield could not see this form, because Krishna gave the vision only to Arjuna. Arjuna could see in the body of Krishna many thousands of planets. As we learn from Vedic scriptures, there are many universes and many planets. Some of them are made of earth, some are made of gold, some are made of jewels, some are very great, some are not so great, etc. Sitting on his chariot, Arjuna could see all these. But no one could understand what was going on between Arjuna and Krishna.

Commentary by Sri Visvanatha Cakravarti Thakur

In that place (tatra), on the battle field, in the body of the Lord (deva devasya), it was impossible to take into account the whole universe. Therefore he saw a part situated in one part of the body at different moments (prati bhaktam, eka stham)--a part situated in the Lord's pore or a part situated in his belly, and in various ways (aneka dha). That is, he saw that form made of earth, made of gold, made of jewels, or measuring fifty koti yojanas, or a hundred koti yojanas or a hundred thousand koti yojanas.