In contrast, the Polo brothers who went to Asia, Niccolo the elder and Matteo the elder, amassed wealth both in tangible and intangible assets.  It was Marco “the voyager” who benefited most from the family business, both as the heir to substantial portions of the family estate, and as a shrewd and cautious — and perhaps tight-fisted — private investor.  His will and inventory of his assets reveal a considerable amount of cash, real estate, and valuables.  Marco Polo traveled for business even after he returned to Venice, but not for long.  After 1300, although he continued to invest in various enterprises, it appears that Marco stayed in Venice.  Perhaps this was due to his advancing age (he turned fifty in 1304), although his energy was most likely taken up by overseeing his interests and local investments, and abo ve all in publicity for his book.  He commissioned numerous copies to be distributed to powerful and influential people.

And:

However, Marco had great difficulty leaving the empire.  The Polos required the khan’s consent not only to be given official leave, but above all to have adequate protection.  As Marco recounts, despite thee riches they had accumulated, they were not free to leave.  By then, the khan had also grown old, and they were concerned that he might die, leaving their fate in the hands of his successor, who may not have granted the necessary permits.  Marco’s account reveals that the three Polos had a subservient relationship with the khan, as they were in the khan’s service and depended on him.  He continually rejected their pleas to return to Venice, as he “loved them too much” and could not accept the idea that they should leave him.

That is all from the new and noteworthy Venice and the Mongols: The Eurasian Exchange that Transformed the Medieval World, by Nicola di Cosmo and Lorenzo Pubblici.