* They are Romance languages. This means they are descended from Latin, the language spoken in the Roman Empire.
* They share a significant number of cognates. Cognates are words that have a common origin and often look and sound similar. For example, "father" in English is "padre" in Spanish, "père" in French, and "padre" in Italian.
* They have similar grammatical structures. They all use grammatical genders for nouns and adjectives, have verb conjugations, and use prepositions in similar ways.
* They are widely spoken throughout the world. These languages are spoken by millions of people on all continents.
In addition to these core similarities, there are also several other connections between these languages. For example, French and Romanian share influences from the Latin spoken in the Roman provinces of Gaul (France) and Dacia (Romania), respectively. Spanish and Portuguese share a common history in the Iberian Peninsula and have influenced each other significantly.
These similarities make it easier for speakers of these languages to learn and understand each other, even if they don't know the other language perfectly.