Пре­об­ра­зуй­те, если это не­об­хо­ди­мо, слово BE так, чтобы оно грам­ма­ти­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

Long ago Teotihuacan was an important religious and economic centre. However, after there _____ a great fire, for some unknown reason all the population decided to leave the city. This happened in 650AD.