Learn Italian: Questa antica usanza si viene tramandando da secoli. - This ancient custom has been passed down for centuries.

While stare + gerund describes an action happening right at this exact moment, venire + present gerund is an aspectual periphrasis used to show a gradual, continuous process unfolding over a long period. It perfectly captures the sense of a tradition moving steadily from the past into the present.

What is the purpose of the si before the verb phrase?

It acts as the si passivante (passive "si"). A custom doesn't pass itself down; people pass it down. By adding si to the third-person verb, the action becomes passive. Therefore, si viene tramandando means "is gradually being passed down" or "has been passed down."

Why is the present tense (viene) used when the English translation says "has been"?

In Italian, if an action started in the past and is still continuing in the present, you use the present tense along with the preposition da (since/for). Because of da secoli (for centuries), Italian uses the present tense viene where English requires the present perfect.

Is there a reason antica comes before usanza rather than after it?