U izvorima se Krupa prvi put spominje krajem 1360. godine. Bila je prostorno mala , ali vrlo čvrsto građena utvrda utvrda na Uni, na njezinoj desnoj obali. Podignuta je na uskoj kamenitoj stijeni koja kao da izrasta iz same Une. Prvi poznati gospodari Krupe bili su Babonići – Blagajski. U drugoj polovini XIII stoljeća, u vrijeme ugarskog kralja Karla, krupska tvrđava dolazi pod kraljevsku vlast. Karlov sin Ladislav 1360. godine daje krupsku tvrđavu sinovima bana Stjepana Babonića Dioniziju i Pavlu. Ovo je prvi put da se krupska tvrđava naziva tim imenom. Uz krupsku tvrđavu braća su dobila i susjednu tvrđavu Otoka i obje tvrđave ostaju u njihovim rukama sve do kraja XIV stoljeća, kada u dinastičkim sukobima oko ugarske krune 1396. godine dolazi pod vlast Vuka Vukčića.
Banska vojska je 1410. godine u ime ugarskog kralja Sigismunda osvojila je krupsku tvrđavu, koja je iste godine proglašena kraljevskim gradom, a kao njeni upraviteljise postavljaju kraljevski kaštelani Zagrebačke župe. Jedan od njih bio je Tibold, koji je bio na zlu glasu u cijelom krupskom kraju, posebno u tvrđavi, pa je i sam kralj Sigismund naredio istragu protiv njega 1418. godine. Međutim, Krupa nije dugo ostala u kraljevskim rukama, jer je Sigismund grad i tvrđavu najprije dao zalog Fridrihu Celjskom, a 1429. godine krupska tvrđava je došla u potpunosti pod upravu celjskih grofova, pa je celjski grofovi 1429. godine nazivaju svojim gradom. Nakon, 1456. godine, tvrđava, kupovinom odnosno mitom, dolazi pod vlast Martina Frankopana. Poslije pada srednjovjekovne bosanske države 1463. godine, iznoseći činjenicu da je Krupa kraljevski grad koji je došao u ruke celjskih grofova kao zalog, Matija Korvin traži da mu se krupska tvrđava preda kao značajan vojno-obrambeni punkt Pounja. Na kraju se Martin Frankopan ipak nagodio s ugarskim kraljem i vratio mu Krupu u zamjenu za Skrad, Bužim, Kladušu i Ostrovicu. Poslije preuzimanja Krupe , kralj je dade na upravu senjskom kapetanu, a kao jedan od njih se 1487. godine spominje Petar Tarnik. Poslije smrti kralja Matije Korvina, Krupa je došla pod vlast njegovog sina Ivana Korvina, koji je krupsku tvrđavu 1498.godine darovao kćerki Jelisavi.
Osmanska vojska se prvi put pojavila pred krupskom tvrđavom 1509. godine, kada je zavedena opet kraljevska vlast. Na mjesto krupskog kapetana kralj postavlja Mirka Turkam. U periodu 1522/23. godine krupska tvrđava je više puta napadana od strane osmanske vojske, a naročito 1523. godine, kada se pod njom našlo oko 2000 konjanika i duplo više pješadije. Opsada je, uz snažnu topovsku vatru, trajala puna četiri mjeseca.
Od 1531. godine njezini gospodari postaju knezovi Zrinski, mada ih habsburški car iste godine u pismu upozorava da ne svojataju tvrđavu Krupu i da ne prave neprilike podanicima Krupe, jer su oni u njegovo ime podređeni bihaćkom kapetanu, a sam grad je, zbog njegove vojno-strateške važnosti, uzeo pod svoju zaštitu. Nikola Zrinjski je smatrao da raspolaže pravom nad Krupom nasljedstvom prema sklopljenom ugovoru s Ivanom Karlovićem o međusobnom nasljedstvu dobara. S obzirom da je grad 1563. godine čuvala posada od 40 kraljevih vojnika, kapetan Ivan Lenković predložio je da krupsku tvrđavu treba napustiti i razoriti. S ovakvim prijedlogom bili su upoznati i Zrinjski, jer su uputili pismo begu Bosne u kojem je bilo napisano: „ Ta tvrđava nije naša. Činite šta hoćete.“
Pod osmansku vlast Krupa je došla 1565. godine i postala sjedište Krupske kapetanije kojoj su pripadali gradovi Otoka, Bužim, Jezerski , Vrnograč i Todorovo. Krupa je još od 1586. godine predstavljala relativno dobro čuvani punkt s ukupno 300 graničara. Početkom XVII stoljeća se taj broj smanjuje na 130, pa se sredinom tog stoljeća krupska tvrđava broji 500 graničara, a od artiljerije je imala dva veća i četiri manja topa. Posadu su činile četiri roda, svi osim martolosa. Čuvana su tri punkta: tvrđava, most u Krupi i kula „Fila“.
Accourding by historicall sources Krupa is first time mentioned in the year 1360. it was a small but tightly built fortress on the right bank of Una River, It was rised on the narrow rocky cliff, which looks as i fit rises from the river itself. The first known landlords of Krupa were the famely Babonics Blagajski. By the end of secondd half of the 13th century, in the time of Hungarian King Karlo, town of Krupa was in Jurisdiction of the King. Kralos son Ladislav in the year of 1360 gives Krupas fortress to the sons of ban Stjepan Babonic, Dionizije and Pavlo. This is the first time, when the Krupas fortress was called by its name. Along with Krupas fortress, the brothers got Otokas fortress, and they both stay in their arms till the end of 14th century, when, in the conflicts of theh dynasty, regarding to Hungarian crown 1396. Krupa comes under authority of Vuk Vukcic
Banus army has in the name of Hungarian king Sigismund, conquered Krupas fortress, in the year 1410,which has been, in the same year, proclaimed kings town. For its governors are named Kings castellans from Zagreb parish. One of them was Tibold, who famous by bad reputation in the whole Krupas area, and especially in the fortress. That even made Sigismund to investigate this man 1418. However , Krupa didnt stay very long in the hands of the king , because Sigismund gave the fortress as a deposit to count Fridrich Celjski, and then in the year of 1429 called Celjs town. Krupas fortress though purchase and bribe , comes under the ruling of Martin Frankopan after 1456. After the falling of medieval Bosnian state, in 1463., by putting out the facts that Krupa was royal city which came in the hands of Celjs counts as a deposit, Martin Korvin asks for Krupas fortress to be given him as significant defensive point of Pounje (area around Una river). At the end, Martin has after all settled with Hungarian king, gave back to him Krupas fortress, and taken as an exchange Skrad, Buzim, Kladusa and Ostrovica. After the kings Matija Korvin death, Krupa came under the rule of his son, Ivan Korvin, who has given Krupas fortress to his daughter Jelisava in the year 1498.
Ottomans army has arrived in front of the Krupas gate for the first time in the year if 1509m when the royal rule once again came to order. To the place of Krupas captain sets Mirko Turk, and soon afte rit comes under the management of Ostrogons cardinal Tomo Bakic, who gives it Ivan Karlovic who attach it to his properties. During of period 1522 – 1723 Krupas fortress was repeatedly attacked from the Ottomans, especially in the year of 1523. in which 2000 horsemen and as double more of the infantry came in front of the fortress. With constant cannon ffire the siege lasted four months.
From the year 1531 its landlords becomes dukes of Zrinski, although in his letter from the same year the Habsburgs Car warned them not to overtake Krupas fortres, and not to makes torubles for Krupas citizens, while they are under the protecftions of the Bihacs captain, who had in mind the towns military-strategic position. Nikola Zrinjski had the opinion that he has the full right over Krupas fortress, by his right in closed dill about inherited goods with Ivan Karlovic. Considering the fact, that in the year 1563. the city was guarded by a crew of 40 kings soldiers, captain Ivan Lenkovic suggested that Krupas fortress should be deserted and destroyed. With this kind of suggestion Zrinjski familiar, what could been seen from their letter: „That fortress isnt ours. Do as you wish.“
The fortress fell under Ottomans rule 1565. From then it had become centger of Krupas Captaincy to which have belonged towns: Otoka, Bužim, Jezerski, Vrnograč and Todorovo. Krupa represented relatively good preserved point with totally 300 border guards, since 1586. At the beginning if 17th century that number comes down to 130, and in the middle of the same century grows up to 232 border guards. In the first half of the 18th century Krupas fortress counts 500 border guardsm and in artillery it had two bigger and four smaller cannons. Crew was made from four divisionsm including everybody but martolos. Three points were heavily guarded: fortress, Krupas bridge and the tower „fila“.
Tekst i slike obradio: Igor Pečenkovic dipl.ecc.hot.
Izvori: JU „Zavod za zaštitu kulturnog naslijeđa Bihać“ popisni registar,“Stari gradovi Unsko-sanskog kantona“ Zavod za zaštitu kulturnog naslijeđa Bihać i Muzej Unsko-sanskog kantona,februar 2009, wikipedia, http://old.kons.gov.ba/