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Lit., "their building" (see next note).
Lit., "schemed" (makara): i.e., they blasphemed by describing the divine revelations as "fables of ancient times" and by refusing to admit the truth of God's existence or of His oneness and uniqueness.
This is obviously a metaphor (Razi) describing the utter collapse of all endeavours - both individual and social - rooted in godlessness and false pride.
This verse refers to a tyrant king who ordered the building of a tower so he can reach the heavens and fight Allah and the angels. Eventually the tower collapsed, leaving the tyrant crushed.
Evil will always devise plots against the Prophets of Allah. So was it with Al-Mustafa, and so was it with the Prophets before him. But the imposing structures which the ungodly build up (metaphorically) collapse at the Command of Allah, and they are often punished from quarters from which they least expected punishment. For example, the Quraish were confident in their numbers, their organisations, and their superior equipment. But on the field of Badr they collapsed where they expected victory.