They used to call this the “AT&T Wiremans Join” but frankly, it’s the best way of joining wire together anyway. If you are joining insulated wire, first strip away about an inch of insulation of both ends.
If you have stranded wire, twist the strands on each wire together and solder them into a single fat strand.
Place the wires at 45 degrees, one over the top of each other – then twist them both together tightly.
I have used this on hard-drawn copper wire and did NOT solder them and the joins stood up fine as antenna wire for a number of years. If you do solder the joint, remember to seal the solder from the elements with self amalgamating tape.
You will find this join is extremely tough.