What was some technology around in the Byzantine empire, like weapons etc.

By far the most effective technological development of the
Byzantines was an incendiary weapon known as "Greek Fire." Its exact composition was a
closely guarded secret and is not known even today, but it has been suggested that it
consisted of a mixture of naphtha, sulfur, niter and quicklime. It was literally "fired"
at an enemy through the means of a siphoning tube. It's major effectiveness was at sea,
as it was lighter than water and would therefore burn on the surface of the water
without being extinguished. It was also fired from the walls of Constantinople on
advancing troops with withering effectiveness. Those struck with Greek fire died
horrible deaths, as water would not remove it or extinguish it. Aside from the
superiority of its geographical setting, the use of Greek Fire was a major factor in the
successful defense of Constantinople on numerous occasions.