Yeah, looks like it did have freelook using the mouse. But even Quake, two years later, still defaulted to vertical auto-aim. Which Marathon didn't do, obviously, but keyboard control was still expected for years afterward. Personally, I didn't start using the mouse until playing Unreal deathmatch in '98.
For Marathon, I used a setup based on the defaults for Dark Forces at the time. Look controls on the numpad (8246, 3 to look up, 9 to look down, 5 to center view). Z/X to sidestep, A/S to glance. Space/Shift for Fire/AltFire.
: I think it did support mouse back in the day but a lot of users back then
: (such as Doom vets) were used to keyboard only. Tuncer certainly played it
: the latter way when he wrote the Marathon guide. I do know for a fact it
: didn't support crosshairs however, so aiming up and down was harder even
: with the mouse.
: Regarding the joke about the mousewheel, I actually play on Windows. >:)
: I do however have the Mac versions too on my hand-me-down Macbook. I got
: Marathon for windows back in 2012, years before I got that Mac you see.