Lazio announce four new signings
Marchetti, who has joined from Cagliari, had an unhappy World Cup last year after replacing Gianluigi Buffon at half-time during their opening game, a 1-1 draw with Paraguay.
The 28-year-old also played in Italy's next two games but they were knocked out after a 1-1 draw against New Zealand and 3-2 defeat to Slovakia.
Stankevicius, 29, joined from Sampdoria, although he played on loan from Valencia last season and for Sevilla for part of the season before that.
Lazio also said on their website they had signed French full-back Abdoulay Konko from Genoa and Bosnian full-back Senad Lulic from Young Boys.
Lazio finished fifth in Serie A last season.