SPQR? Who?

[Duguntz]

Without Rome, zorostrianism would not only dominate Eastern europe, but would be the dominant religion in the world (note... not the ONLY one, but the DOMINANT, just like cristianity today), Road system would be much less developed, western architecture would have more arabic and hellen influence than latin (like today's southern france and mediteraneen states) Northen france would be totally diffent than southern, probably keeping much influence from celtic past. there would be MUCH more red-haired people in England and france, not having entered in contact (not is too big a word, but let's say much less) with the Latin gene. Americas would have been discovered, though later, as mentality and ideology wouldn't have been the same. but evolution is a race wich cannot be stopped, so at somepoint, european woulld have wondered still what lay behond that ocean.

[Skuda]

IMHO there will be no concept of European civilization but Europe could be home to some very different civilizations - Celtiberian, Celtic, Italic, Germanic, Thracian etc. I believe though that without Rome Celtic culture would have a huge potential and MAYBE some of the celtic nations could unite most of Western Europe.

Of course there will be no christianity and islam or they would be something like Buddhism on Far East - only part of religious system

[Zradha Pahlavan]

at somepoint, european woulld have wondered still what lay behond that ocean.

Who says a European would have to have discovered the new world? Why not an explorer for the Sassanid Empire? Or the Chinese?

My half-assed theory up until the Renaissance is here:

Spoiler Alert, click show to read: 

1. Samnites take over Italy.
The Samnites most likely wouldn't have had the influence and reach of Rome, but if I remember correctly they did have a good military along similar lines to the early Roman army, and Rome was the main thing standing in their way. Assuming that none of the other powerful Italian factions took Rome's place and slapped them around a bit, the Samnites and their buddies would've been the guys in charge.
2. Pyrrhus and friends invade.
He wanted to emulate Alexander the Great, but in the west. Due to the Samnites position I'm not so sure that they would've been able to muster the resources that Rome did against the Epeirots, thus allowing Pyrrhus to slap them around get a good base in Italy. Then he'd probably try to take over all of Italy and make forays into Celtic lands.
3. Celts get pissed off.
The Celts would respond by raiding the Epeirots' new territory and by helping out any little Italian groups that tried to free themselves of Epeirot rule, but then eventually they'd go back to beating on each other some more.
4. Carthage takes over Iberia, since no one but the Iberians care.
5. Carthage and Epeiros eventually get into a big fight over Sicily.
Both sides butcher each other over land, Carthage gets some victories at sea. Eventually Carthage gets Sicily.
6. Carthage makes a pass at Italy, but it gets its ass handed to it in this venture.
7. Carthage goes for Epeiros itself, gets some Illyrians to help it out, and smashes up some cities, but is eventually pushed back.
8.Wars go on for a while, Carthage has problems keeping Iberia under control, but eventually they get support from Gaul and make a naval invasion of Italy. Epeiros begins to fall.
9.Eperios gives up and never again rises to greatness.
10. Carthage tries to subdue the continually rebellious Iberians, the Numidians, and the Gauls. Doesn't work. Carthage doesn't have the military might to keep expanding against numerous people who would rather not be under Carthaginian rule.
11.Some of the Gallic tribes unite into a feudal confederacy, allowing them to gain control over Gaul and they go after Britain and the weakening Carthage.
12.Hordes from the steppes migrate into Europe and take over the eastern part. Greece and Italy are nearly overrun. Carthage manages to recover most of its losses, and Carthaginian elephants prove very useful against the heavy steppe cavalry. Macedon also holds out, but becomes too weak to fend off the other Greek powers.
13.The invaders turn on Gaul, and ravage the area but are eventually stopped.
14.Parthia has skirmishes with the remaining Greek Empires, but doesn't make it to the Mediterranean.
15.The Sassanids take over where their Parthian predecessors left off, crushing all opposition in central Asia and getting themselves into a bloody war with the Egyptian dynasty. They take over many areas of Greece and eastern Europe.
16.Egypt and North Arabia fall to the Muslims.
17.Carthage gets taken out by the Muslims, Iberia and Italy become fully independent again, but many aspects of Carthaginian culture have been incorporated into their socieities.
18.The Muslims take Iberia, but the Gauls do not give way to them.
19.The Sassanians hold back the Muslims in central Asia.

[Brennus]

There doesn't appear to be much faith here that Celts could have developed into nations states independently (With the exception of Skuda, good point BTW).

Where's Oudysseus and Bobbin when you need them?

[Macilrille]

Working on EBII I believe.

Competetion between nation states that drove each one to excell and exploit and develop all available resources was what made Europe dominant.

David Landes elaborates in his "Wealth and Poverty of nations", and I by and large agree with him, not his opponent André Gunder frank whose book was so unmemorable that I forgot its name.

[Skuda]

Western European Celts had a rather technologically advanced culture and, in some regards MORE technologically advanced culture than the Roman (remember steelmaking)... still they didn't have stable states. But if we take Archaic Greece they didn't have such states either. I think Celts needed two or three more centuries to build more or less successful feudal society... and don't forget Roman divide-et-impera policy in Gaul in II-I century BC. Maybe without these efforts Arverni or Aedui could succeed earlier.

We have an example when tribal society ALMOST succeeded in building advanced state - Dacians. If they didn't have Trajan's Empire against them...

[Apázlinemjó]

Without Rome we would get a warlord named Jesus Christ, who could unite the whole Earth under one banner against the Borg.

Naaah, but I'm sure that without Rome there wouldn't be Christianity nor Islam.

[Hax]

I think the rise of Islam was indeed influenced by the existence of Christianity. When Muhammed experienced his "visions", his wife Khadija brought him to a Christian priest. I don't think it's really that important, though. Perhaps Islam would've existed, but under another name. Don't forget that Zoroastrianism was hardly a religion that liked proselytise the way Christianity and Islam did. Perhaps Buddhism would've spread west as well, creating a new form of Persian Mahayana. I don't know, it could've gone pretty much anywhere.

[Hannibal Khan the Great]

I think we're all forgetting about the Germanic tribes. They, under warlords like Ariovistus, made devastating assaults into Gaul that were only stopped by the huge Roman armies... If Caesar hadn't been there to stop him, maybe Ariovistus or another warlord could have created a powerful enough territory to unite many tribes under one banner. They would have been largely Celticized, rather than Romanized as in history. Of course someone else could have made some major incursions as well.

[jirisys]

I think we're all forgetting about the Germanic tribes. They, under warlords like Ariovistus, made devastating assaults into Gaul that were only stopped by the huge Roman armies... If Caesar hadn't been there to stop him, maybe Ariovistus or another warlord could have created a powerful enough territory to unite many tribes under one banner. They would have been largely Celticized, rather than Romanized as in history. Of course someone else could have made some major incursions as well.

That's preference (the celt wants the celts to rule the world)

anyway, we would have never existed (if rome were not to exist, the world would break into a million pieces... in one of them would be cute wolf)

~Jirisys (why not Jebvijetar too?)