I'm reading about Battle of Leuctra and there is a description of the initial meeting of the Thebans and Spartan lines. The description states that a large number of Spartans were killed more or less instantly upon impact of the phalanxes. Was this because the Spartan formation was not fully formed and their lines were penetrated or did the sheer force of a 50 man deep formation just overwhelm them?
If it was the force of the impact would this have crushed the front row of the Theban rank also?
The first ranks in a phalanx were called promachoi or promachos and were basically the hardest, toughest men from the local tribes. They wanted to fight.
Is it Xenophon's account? You need to take it all with a pinch of salt. Even Diodorus'.
The oblique flank was the first time that it was used, so 8-12 ranks of the Spartan right couldn't have withstood the 50 ranks of the Thebans. No doubt the front ranks of the Thebans suffered heavy casualties.
Hoplite warfare is essentially a mass shove - in the classic view anyway. Some are now challenging this but it is mainly judged there was mass shove or othismos and one side eventually was pushed back and fled.
Best way I imagine it is imagine being the promachos - you don't have a choice whether you get pushed forward, with 7-11 other heavily armed men pushing you with their aspis shields, you're going forward.
Now, imagine it's not 7-11 men, but 49 pushing you forward, but only 8-12 men trying to stand up to that - you're definitely gonna go forward. Now, if you can avoid taking a dory/xiphos thrust to any of the vital areas, and manage to stay stood up, you probably would survive. The mass push at Leuctra would have been rather brief.
So yes, the front ranks of the Thebans probably would have suffered high casualties. That's why they're the promachoi.
Hope this helped!