<p><pre><code>  India, China and the Arabian peninsula take one hundred million sesterces from our empire 
  per annum at a conservative estimate: that is what our luxuries and women cost us. For 
  what fraction of these imports is intended for sacrifices to the gods or the spirits 
  of the dead?
  — Pliny, Historia Naturae 12.41.84. (https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Indo-Roman_trade_relations#Establishment)
</code></pre>
Like the rest of the world, the Romans wound up using specie when importing luxury goods from south east Asia and China.  Aside from possibly glass production, there were not many goods produced in the Mediterranean that could survive transit down the Red Sea, around Arabia, and across to India on the monsoon, or overland, which were significantly higher-quality than what could be produced locally.  Whereas silk, spices, incense and the like are high-value, low-bulk items, which can travel well, and are unique products not found in the Mediterranean.