Fort and other words beginning with that formidable foursome of letters have a strong heritage going back to ancient Latin. Here’s a discussion of fort and the fort- family of words.
Fort derives, through the identically spelled French word meaning “strong,” from the Latin term fortis, which has the same meaning. (That word is also the origin of force.) The variant fortress is ultimately from the Latin term fortalitia by way of the French word forteresse, meaning “strong place.” (The suffix -itia, denoting condition or quality, is also sustained in duress and largesse.) Another noun referring to a stronghold is fortification; the verb form is fortify. Fortitude refers to the characteristic of strength.
Another word, forte, has two distinct meanings based on convergent evolution from Latin. The Italian term forte, which shares fort’s etymology, is used as a music instruction in English to indicate that a composition, or part of it, should be played loudly.
The Italian term also appears in the instruction pianoforte, meaning “soft and loud.” (Piano is from the Latin word planus, meaning “even, flat, smooth”; later, the Latin word and its French descendant acquired the additional sense of “soft.” The musical instrument called the piano was originally referred to as a pianoforte because one could produce both quiet and loud notes on it.)
Forte, from the French word fort, meaning “strong point” (as of a sword blade) and acquiring the e in imitation of the Italian word, came to refer to a person’s primary skill or talent, though it still refers to the part of a blade near the hilt.
This site generally does not discuss pronunciation, but note that the common pronunciation “for-tay” erroneously reflects the Italian term, not the French word for “strong point,” which in French is pronounced “for.” However, the two-syllable punctuation is ubiquitous, and you are likely to confuse people if, when using it for this sense, you pronounce it “correctly” (“fort”).