Eruvin 17a and Eruvin 17b, finishing up our discussion of when we can use walls made up of just rope or just pickets, leading into a discussion of whether the definition of the eruv happens at Shabbat for that entire Shabbat, or problems that arise can be problems even for that Shabbat, and then ending the chapter with leniencies for armies, including not needing to make certain eruvin. Then starting the next chapter, about the posts we make to allow drawing from a well.
