Did Starswirl create the portal before or after they banished the Sirens?

[Skytower 71]

In the show it was Starswirl and the rest of the Pillars that sent the Sirens into a portal, but it was implied in the show (and shown in the comics) that he put them through the portal that Sunset and later Twilight used.  I wonder if he created the mechanical portal first and came up with the banishment spell as a by product of his portal design, or if he built the mechanical portal afterward, possible as a way of finding out where the Sirens had gone.  It might be that it was only after the Sirens were sent into the portal that Starswirl realized that banishing them to another world meant that another world had to deal with them.  

[sweetolebob18 728]

Well since Starswhirl was trapped in the portal after using it on his friend, I'm guessing it was used on the Sirens first & then he realized the mirror idea was flawed. 

[Skytower 71]

15 hours ago, sweetolebob18 said:

Well since Starswhirl was trapped in the portal after using it on his friend, I'm guessing it was used on the Sirens first & then he realized the mirror idea was flawed. 

Didn't think of that.  Maybe the mirror portal was a prototype he realized wouldn't work.