Does anyone know when the Dunmer strongholds were built? I was wondering if they would have been built before, during, or after the War of he First Council.

I think they were built during the Nord Invasions.

No such info.

edit:

Before the War of the First Counsel, they feature in Poison Song.

http://www.imperial-library.info/mwbooks/poisonsong.shtml

Thanks for the answers. This clears up the question I had.

But is that before Velothi High Culture, or after the fall but before the First Council?

We know that at least Kogoruhn was around before the War of the First Council, but it didn't have a propylon chamber like the others did. Still, it had the same architecture as the others.

We do?

I'm no lore-meister, and am just reading from memory here, but Kogoruhn is the 'Sixth House stronghold', right?

And the Sixth House was destroyed after the War of the First Council (see Poison Song etc.). So it's unlikely that they would have had time/money/manpower to build an entire massive stronghold after their obliteration.

So, an educated guess (however boring) suggests that, yes. (Of course, I could have my facts wrong.)

Most Sixth House bases are scavenged, but that point stands for the rest of the houses. I knew I was forgetting something.

While Kogoruhn was indeed scavenged by the Sixth House, it seems that it was in their possession before House Dagoth fell, as evidenced by the House Dagoth Cup and tomb of Dagoth Morin beneath the stronghold. In addition, Hasphat Antabolis said that it was their clanstead.

as i see they were built during the invasion of the Nords and they built these stronghold to keep the Nords who would try to stop them.