The Greeks and Romans mostly got soap-like cleaning substances from the wider Mediterranean and Near Eastern world, where early soap making was already known; but for personal bathing, they often preferred oils and scrapers rather than soap itself. In Rome, soap was also associated with Gaulish practice and later with specialty cleansing and laundry uses, not everyday body washing.

What they used

Ancient people commonly made soap by combining fats or oils with alkaline ash or lye, and some of the earliest evidence points to Mesopotamia and nearby regions. Greeks and Romans learned about these kinds of mixtures through trade and cultural exchange, then used them more for cleaning textiles, hair, and certain cosmetic or practical purposes.

Roman bathing habits

Romans famously liked baths, but they usually did not rely on soap the way modern people do. They bathed in water, rubbed on olive oil, and removed dirt with a strigil, which is why soap was not the main bathing product in daily Roman life.

Where the idea came from

There are later legends tying soap to Mount Sapo or to Greek stories, but those are not solid historical origins. The more reliable picture is that soap developed gradually across ancient civilizations and spread through trade and regional contact.

In one sentence

So, the Greeks and Romans got soap from older soap-making traditions in surrounding ancient cultures, but they usually used it more for cleaning fabrics and hair than for washing their bodies.

TL;DR: Soap didn’t start as a Roman bathroom staple; it came from older ancient cleaning traditions and was used differently than it is today.