Formatted /system without backup ROM or SD Card slot
Possible solutions, from the least to the most effort:


Directly adb sideload a working ROM from the PC - provided that your current recovery supports it. Probably not, as CWM is very outdated;
adb push a working ROM from the PC into your phone storage, then flash it using the recovery;
Flash TWRP recovery, then adb sideload a working ROM from the PC;
Flash a factory image via fastboot and start over, as @acejavelin already suggested.


All methods require a PC with working adb and/or fastboot drivers.