Roman Emperors Constantinus II and Constans outlawed same-sex marriage on December 16, 342 C.E. (Theodosian Code 9.7.3)

Roman codes of laws were the Law of the Twelve Tables of 450 BC, the Gregorian Code (Codex Gregorianus) of 291- The Hermogenian Code (Codex Hermogenianus) of 291-4, the Theodosian Code (Codex Theodosianus) of 429 and the Corpus Juris Civilis (Body of Civil Law) also dubbed the Justinian Code of 534.

They had sea walls and land walls to protect invaders from entering

I assume you mean the Walls of Constantinople. They were originally built when the city was founded, in the 7th century BC. In the 5th century AD, the famous double line was constructed (the Theodosian wall). These were often imitated, such as at Caernarfon Castle in Wales.