Carseats in taxi

I have never ever heard of, or seen a taxis with carseat. And since many carseats must actually be tethered in ( not just seat belted) to make them save, and I have never seen or heard of a taxi with a tether bolt so your own seat wouldn't be that safe either. Now, at 2.5 yrs old, it your child is big enough( and yes I know this is not ideal, but perhaps better then nothing) consider bringing a car BOOSTER seat, some of them are much smaller and easy to carry, and none of the no back type I have ever seen require a tethering strap, just seat belt in, so easy to put in any vehicle with a seat belt. It may come in handy at restaurants etc for sitting at the table also.
Ideally bring nothing and only use public transport, but, I do understand after a long flight and with a late arrival a taxi is the way to go.
I don't know about Italy( but I imagine it is the same) , but you do know in Canada taxis and buses are carseat exempt. Doesn't mean safe, but what can you do?

We've just used the seatbelt. We also thought we were horrible parents, but there's now way to get a car seat properly fitted into a taxi.

I have a personally tested solution: purchase a RideSafer Travel Vest made by Safe Traffic System, Inc. Chicago, IL. 773/296-6850. http//www.safetrafficsystem.com. I bought ours from a website I found via Google.
This product is great! We travel a great deal and our family has 6 of them for our 2 kids. Our nanny received a set. My husband has two for his car and we keep a set for our trips to: Italy (2 times), Germany (1 time), NYC, Chicago, Santa Fe, Honolulu, etc. They're not 'allowed' for the airlines but we can quickly snap them into taxis, rental cars, grandma's car, etc. They come in two sizes and so far we've only needed the smaller size. We pack them in our luggage right on top so that we yank 'em out and set them up quickly.
Here's another gadget for traveling parents: Kaboost: a plastic contraption that lifts an adult chair up so that a toddler can sit comfortably (no booster seats in Europe, either!). www.kaboost.com

you will not find a taxi with a carseat in Italy easily...you CAN buckle him in in the middle if you feel ok with it...the law in Italy is very vauge about it and says they must be in aa car seat or seat belt "if there is one available" BUT....honeslty, just buy a backless booster and ditch it when you're done with it. It's not a big deal and you just check it with the bags on the airplane. You can buy them (Graco and Cosco) at Target, Wal Mart, etc. for under $20. My kid is 7 now and over 60lbs...and, recently, I let him in a car in Italy with no booster for the first time...and I was still freaking out about it...not worth the stress ;-)

Thank you for all your helpful responses. We took our son in taxis in Mexico, unnerving, yes. Often there weren't any seatbelts at all, never mind ways of strapping in a car seat or booster. I'm mostly concerned about breaking Italian laws or being denied a ride. The situation is not ideal, I may look into getting a travel tether which seems reasonable to lug around. Thanks!

you will not be denied a ride in Italy...it is still common to see kids (and infants!) on a lap in the front seat in Italy. Do whatever works for your personal comfort level.