The Visvia-class Defence Platform is a space structure available only to the Empire of the Hand in eras 1-5. It's armed with 40/8 dual megamaser cannons and 4/4 tri-heavy megamaser cannons
The development of a heavy defence platform was made at the urging of the then Senior Captain Voss Parck in anticipation for the invasion of an unknown extra-galactic alien race (that wouldn't be arriving for another 15 years). The Visvia is also one of the many examples of the high quality manufactures of Chiss-Imperial technologies; strong durable armour provided by the Chiss and firepower that rivals the second variation of the Golan Defense Platforms utilized by the Imperial Remnant. It was also accompanied with four heavy tri-cannons the size of a small starship that could cripple even an Imperial I-class Star Destroyer in a single volley.
The Visvia is one of two space defence platforms utilized by the Empire of the Hand, the other being the Brask-class Tactical Defence Station. Unlike the Brask however, this structure is designed to fight head-to-head with any ship. However, it is this same reason why the Visvia is the most expensive item available to the EotH and the most expensive space structure in the entire game, costing 10,000 credits.
Whilst the heavy tri-cannons are very effective against Heavy Frigates and Capital Ships, they struggle to target and hit Corvettes and have next to no defence against fighters. Hiding several anti-fighter ships under the Visvia not only gives the Visvia the cover it needs against fighters, but the corvettes themselves can't be targeted because they're under the Visvia; meaning the platform itself must be destroyed to attack the ships which isn't easy due to dual and Tri Megamasers.
In short, the Visvia is an expensive but efficient way to dispose of enemy Frigates and Capital Ships during an enemy attack.