What sort of structure was the “tower” (Gen 11:3)?

And what significance is there in the observations that they wished to build with brick and “slime” (Gen 11:3; and what is that)? While this is not entirely clear from the text itself, it is very likely to be a ziggurat, with the identity supported if not confirmed by the description of the materials as being brick and “slime,” i.e., “tar” in the more modern translations, also identified as “asphalt” and “bitumen,” which are both in Strong’s gloss of חֵמָר, chemar. The building materials, even at the time of Moses, might have been known to break down relatively quickly, at least compared to stone, and might have already been thought to exhibit the vanity and ephemerality of the greatest works of man.