In 1.0, pre 1.18ish, as Orophin said, any player could virtually learn any ability and even use traits from other classes.
The Marauder may have had an Intimidation trait that increases enmity.
The Pugilist may have had an increased healing received trait (that may have been broken).
A Gladiator may learn a handful of abilities such as Obsess, that helped him generate enmity and mitigate damage toward one target such as a strong foe, but lowered his defense against other enemies.
A Marauder who was stationary gained a buff called Steadfast, which if I'm not mistaken, increased his parry rate and caused several of his single target attacks to become cone attacks (Skull Sunder and Brutal Swing) and thus secure multiple mobs, but positioning was key since moving would remove this Steadfast buff.
Anyone who was supra-serious about tanking would grab as many enmity and mitigation abilities from each class and couple up the traits where they could. They might also allocate their attributes toward Vitality, as back then, it appeared to affect max HP and physical defense. A lot of folks would just eat magic attacks instead.
Even casters who developed their shield arm could generate lots of enmity and keep themselves sustained. A conjurer or thaumaturge might blast enemies with an initial AoE attack or debuff, use Sentinel/shield abilities to defend themself, then heal themselves while relying on Shock Spikes and other counter damage to take down enemies. Most mages that I came across did not invest in Vitality with the intent to tank. They usually wanted their spells to kill enemies before needing to take a beating.
There was no enmity bar and it was uncertain how much enmity some moves performed or how far ahead the tank was. Many players were encouraged to have some self sustaining abilities such as Second Wind, Cure or Sacrifice, in addition to some enmity management like Decoy and Quelling Strikes. Self-healing and mitigation abilities were pretty potent and it reduced the need for a dedicated party healer. Oh yeah, and casters could run and cast without canceling their spell, which probably was pretty overpowered.
Couldn't advise you on 1.18+ tanking. I do recall an enmity blinker by then letting you know if you were getting close to taking enmity.