There were giants, Nephilim. Before the flood:

⁴ The Nephilim were on the earth in those days, and also afterward, when the sons of God came in to the daughters of men, and they bore children to them. Those were the mighty men who were of old, men of renown.

Genesis 6:4 (NASB95)

And after the flood:

³³ There also we saw the Nephilim (the sons of Anak are part of the Nephilim); and we became like grasshoppers in our own sight, and so we were in their sight.”

Numbers 13:33 (NASB95)

None were on The Ark. Which means, the flood killed all mankind, but it seems some Nephilim survived.

They had to be very large giants in size, not just in high regard, but actual size. This means the Nephilim were never mentioned to be totally killed off in the flood.

Which allows for their tech, pharmakeia and so on, to have a means of carry over post flood. Many feel they spent time in Egypt.

The sons of Anak were Nephilim. Also known as Anakim:

Where can we go up? Our brethren have made our hearts melt, saying, “The people are bigger and taller than we; the cities are large and fortified to heaven. And besides, we saw the sons of the Anakim there.”’

Deuteronomy 1:28 (NASB95)

Also others:

(The Emim lived there formerly, a people as great, numerous, and tall as the Anakim.
Like the Anakim, they are also regarded as Rephaim, but the Moabites call them Emim.

Deuteronomy 2:10-11 (NASB)

All the same, they were a people, who could suffer defeat at God’s will:

a people as great, numerous, and tall as the Anakim, but the Lord destroyed them before them. And they dispossessed them and settled in their place,

Deuteronomy 2:21 (NASB95)