What is a scroll?

Revelation 5:1 (ESV)

1 Then I saw in the right hand of him who was seated on the throne a scroll written within and on the back, sealed with seven seals.

We may picture in the eye of our mind a stick with a lengthy piece of parchment wrapped around it (and the stick perhaps removed). A reader would then unroll the parchment to read a column of print (e.g., Luke 4:17, Luke 4:20), then begin rolling the loose end as he unrolled more columns for reading. In John’s time a scroll was kept closed with a string (or a number of strings, depending on how high the scroll was).