A memory array comprises laterally-spaced memory blocks individually comprising a vertical stack comprising alternating insulative tiers and conductive tiers. Channel-material strings of memory cells extend through the insulative tiers and the conductive tiers. A ring is around individual of the channel-material strings in at least one of a lowest of the conductive tiers or a lowest of the insulative tiers. Individual of the rings have a top that is below all of the memory cells. Other embodiments are disclosed.